This is what I did, recently:
Antec P182 case (I like the looks, and with some extra cooling I haven't found it getting warmer than 42 degrees C while playing WAR)

mobo: Asus P5Q pro
processor: Intel core 2 duo E8500 3.16GHz, etc, etc.
sound: Creative soundblaster X-Fi Xtreme music
video: Asus ENGTX260 896MB, etc etc
2x2GB Kingston memory
hd: Samsung spinpoint 1TB hd
Scythe Ninja 2 cooler
620W CoolerMaster power supply
Windows Vista home premium
plus cardreaders, 2x dvd writer, etc
Cost 1369 euro including having it put together etc (I'm not much of a DIY guy), which is GBP 1002, so assuming the parts will be slightly cheaper there than here, and you save money by putting it together yourself, this should fit your budget nicely, and you could even tune it up just a little bit more.
The game runs smoothly at max settings, only loading screens still take a while (around 5-10 seconds, which is longer than I would have expected) - no choppiness ingame so far, not even in busy keep sieges. Except for the occasional CTD or black screen when tabbing, it all works as expected, actually!
Oh, piccie of the case:
