First a big Vadim
Second what you going to be using it for as this will help to deside what parts but the first thing that strike me is more memory for a lesser power supply.
It will be used for a bit of everything really! Work, playing games, watching films etc. I thought about a lower power supply but really 20 quid difference between an 850 watt power supply and a 1000 watt, thought I might as well put the 1000 on.
First, I'd consider Antarctic air cooling rather than liquid cooling, unless that's a must for your build -- you could put the price difference into your components and unless you're overclocking (or adding additional graphics cards for SLI later, which'd require a different mainboard anyway) then air cooling should keep things running well within acceptable temps/sound.
You might do better to go for higher density memory, rather than 4 1GB sticks.
Depending on availability, I'd wait for nVidia's 9800 GTX+ (basically a more efficient, higher-clocked version of the 9800 GTX which won't cost much more), or if absolute highest game performance isn't necessary (i.e., GTX 280) you could consider the Radeon 4870 in place of the GeForce 9800.
I'd also add a second physical hard drive -- always better to have Windows on one drive and games/etc. on another, IMO (and it makes reinstalling Windows much less of a hassle), or just for backup use considering the low cost per GB of hard disks.
Finally, higher wattage doesn't necessarily equal a better PSU -- you might do just as well (and save some pennies) with one of the 600-700W Real Power units.
Here would be my suggestion based on your posted spec and budget:
The most important thing about speccing out a system where budget is your top priority is knowing where to skimp and where to indulge.
PSU is the first thing; even a huge skulltrail system with 5+ hard drives, two graphics cards, two cpus and 8gb of memory will only just about consume 1000w of power (when choosing a psu for a high end platform like skulltrail the most important requirement is the capacity of the individual rails as opposed to the 'accumulative' capacity of the whole unit). So for system of this size, 700w is more than sufficient.
4gb of memory is more than enough and it's much more economic to get less sticks but of larger iterations (i.e. 2x 2gb sticks instead of 4x 1gb sticks).
I've chosen you the cosmos S case as it's one of the best for air cooling, but the system should perform just as well in the TJ05 if you particularly like that case.
When going for a lower-class CPU such as the q9450 it would be a crime not to complement it with overclocking! And the Antarctic air cooling package will be sufficient to get a decent overclock out of the CPU. You chose water cooling in your original spec, but it's fairly pointless to have watercooling if you're not going to have overclocking as well.
As quite rightly suggested by Fearless Hero, it's better to have your OS on a smaller, faster drive and put your games on a larger drive. Therefore i have slected you a 300gb velociraptor and a 750gb WD Caviar GP drive.
I also managed to fit the gtx260 card into the budget as well, which is the 2nd best graphics card on the market today
Case: SILVERSTONE TJ05 Black CASE (NO PSU)
Window: none selected
Cabling: Standard Cable Management
Cooling: Antarctic Cooling (3-5 Fans digital controlled+VGA/HD Cooling)
Airbrushing: none selected
Fans type: Blue-LED fans
PSU: Coolermaster Real Power M700W Modular PSU
Motherboard: ASUS Maximus Formula (Intel X38 - 1600/1333 FSB)
CPU: Intel Core 2 Quad Q9550 Retail (4x2.83GHz 1333FSB 12Mb)
CPU Cooling: Scythe Infinity Heatpipe Cooler (all CPUs)
Memory: (2x) G.Skill DDR2-800 PK 2x2048MB CL4 Dual Channel Kit
Graphics: BFG Nvidia 280GTX OC 1024Mb PCIe 2.0 HDCP
Hard Drive: 1Tb Samsung SpinPoint F1 HD103UJ 7200 32mb Cache SATA II
Storage HD: none selected
Optical Drive: none selected
Optical Drive 2: Lite-On LH-2B1S Blu-Ray SATA DVDR Black
Floppy Drive: Lian-Li 3.5" Aluminium 25 in 1 Card Reader and USB (Black)
PCI card: none selected
PCIe Device: none selected
Sound Card: Creative 7.1 X-FI XtremeAudio PCIe OEM
Operating System: Windows Vista Home Premium 64 bit DVD OEM
Secondary OS: none selected
OS Extras: Support CD (Genesis CD)
Building: Saver Build (10-20 working days)
Overclocking: Extreme Overclocking (10-50% - CPU/Memory/VGA) (NOT RECOMMENDED)
Warranty: Premium 2 Year RTB Warranty and Lifetime Support
Free T-Shirt: Vadim Computers Baseball T-Shirt (M)
Packaging: Heavy-duty packaging (Full Towers - 80x80x40)
Highlights include; The best graphics card of the day the NVIDIA 280, a quad core processor at 2.83 GHz, 4 GB's of RAM and a Blu Ray Burner and Player! All at an amazing price of £2330 including VAT! And this is all before overclocking!
Thanks guys, those specs are great. I went with the one hard drive as ive got an external one already which i will use to store anything that isn't being used much on. so then when i do need it, i will just copy the files across to the main hard drive and vice versa.
Heres my effort...I included the fastest dual core as i think quads are still not fully optimised yet...and should goto nearly 4ghz after overclocking!!
280gtx also inc...
£4 over budget.....
Custom Fusion-CS-Intel-775G2 system 43825
Case: SILVERSTONE TJ07 Black CASE (NO PSU)
Window: none selected
Cabling: Standard Cable Management
Cooling: Antarctic Cooling (3-5 Fans digital controlled+VGA/HD Cooling)
Airbrushing: none selected
Fans type: Non-LED fans
PSU: Coolermaster Real Power M700W Modular PSU
Motherboard: ASUS Rampage Formula (Intel X48 - 1600/1333 FSB)
CPU: Intel Core 2 Duo E8500 Retail (2x3.16GHz 1333FSB 6Mb)
CPU Cooling: Scythe Zipang Heatpipe Cooler (all CPUs)
Memory: G.Skill DDR2-1066 PK 2x2048MB CL5 Dual Channel Kit
Graphics: BFG Nvidia 280GTX OC 1024Mb PCIe 2.0 HDCP
Hard Drive: 1Tb Samsung SpinPoint F1 HD103UJ 7200 32mb Cache SATA II
Storage HD: none selected
Optical Drive: SONY-NEC Optiarc AD-7203S SATA 18x DVDRW Black OEM
Optical Drive 2: LG GGW-H20L Blu-Ray RW-HD-ROM Black SATA
Floppy Drive: none selected
PCI card: Asus WL-138gE Wireless PCI Adapter
PCIe Device: none selected
Sound Card: Creative 7.1 X-FI ExtremeGamer
Operating System: Windows Vista Home Premium 64 bit DVD OEM
Secondary OS: none selected
OS Extras: Support CD (Genesis CD)
Building: Saver Build (10-20 working days)
Overclocking: Safe Stable Overclocking (5-40% - CPU/VGA)
Warranty: Deluxe 1 Year Collect and Return-Onsite Warranty (+1 year RTB)
Free T-Shirt: Vadim Computers Baseball T-Shirt (M)
Packaging: none selected
£1,960.94 £1,960.94
And the Antarctic air cooling package will be sufficient to get a decent overclock out of the CPU. You chose water cooling in your original spec, but it's fairly pointless to have watercooling if you're not going to have overclocking as well.
