Id dump the flatscreen monitor and go for a CRT instead.
The Athlon XP is *THE* fastest processor you can get at the moment. Overclocking it is a little hard unless you've got a steady hand and a conductive pen, but ive heard reports of the core hitting 1.8ghz.
512 mb DDR RAM should be enough..consider not only PC2100 but also the next one up (cand remember what that one is) - i know its available in places.
Motherboard wise you might want to consider the Epox board or the Abit KG7...these boards have generally got the highest level of performance/speed out of the crop. Plus the abit board has 4 DDR slots instead of 2 or 3.
Hard drive wise the maxtor diamondmax +60 or the IBM GXP60 are both excellent buys. My experience with Western Digital harddrives is that they wear out pretty fast. Seagate are best avoided unless you go SCSI.
Upgrade the PSU to 350 watts...you'll probably need it.
GF3 is a bit of a waste of money at the moment..but its your decision. IMO the graphics card bizz moves so fast now any investment you make will turn to poo 6 months down the line.
Firewire...do you need that? or can you make do with USB? your choice.
Audigy soundcard? if its anythign like the 1st revision SBlives then avoid. Maybe a videologic Sonic Fury might be worth a look.
If you do rendering

..and want to go into that stuff on a PROFESSIONAL level, get a dual machine. Since most game engines arent even multithreaded dual processors wont help you much, but most 3D apps are and will benefit greatly from 2 processors (2 ahtlons mind you..P3's have a crap bus and p4's...well...are laughable really)
Hope this helps.
All in all..you can put together a monster system for about £1300 these days (minus software licenses - bleh) ..which isnt too shabby at all.
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AARGGH!!
My Normals' Flipped!!