CPU - Save the 5 or so quid and go OEM as your getting a separate heatsink
Copied and pasted wrong, is an OEM chip :-)
GFX - Get a normal high clock card not a XXX card. They are generally not worth the money (£30 more for very little gain)
So im noticing :-)
Memory - 4 MB any PC6400 will do. 2Mb wont be enough given 6 months way things are going.
Yah going for the 4GB set
Monitor - REALLY REALLY consider getting a 24" instead. Price difference is less than £100 to a acceptable 24" TFT and will give you 1080p compatibility, giving you more future proofing as 1080p will probably become a graphics standard for a long time. Scan have the PLE2403WS-B1 on today only over Easter, which is meant to be a ok/good monitor although the Professional version is better (for £40 more).
Really trying to save the pennies a bit, am used to a 19" so the 22" will be ok I think.
OS - Get Vista 64 Bit. 32 bit is really on its last legs due to the memory limit, pity XP 64 wasn't as wildly adopted
Whilst id like to 64bit games particularly dont seem to get much of a benefit yet.
This will save you some money in some areas and spend it in much better ways.