quick look .. its ok ..
go for more memory and a sata III hard drive ... £765


but...
i would personally change...
the graphics card,(prefer ati)
the power supply,(like corsair)
the case,(personal choice)
the memory,(64 bit system might have 16gb)
the hard drive,(sata III)
the display, (asus led)

oops £899 bugger i can spend money easily enough

all depends on what you want to do with it ..
i have always spent more than i have budgeted for, building your own is fun and you can always add another graphics card or a better on in a year or so .. had mine 3 years now and spent £900 in total on it.. just started to tell its age on bf3, but thats just the graphics card ..

mate has just spent £250 on a graphics card and bf3 is awesome on his 24" display
although he built his 2 years ago and spent £1500 on an i7 tripple channel system with ssd drive .. boots up in seconds though