The KT400 is a slug. Really, the Nforce2 is the only viable option for the AMD platform at this time. Current Intel motheboards all have serious drawbacks and I'd avoid that route altogether, at least until the Canterwood and Springdale launch in May.
Replace the videocard with a Radeon 9500 Pro or 9700. The Ti4800 is just a Ti4400 with AGP 8X compatability, and the card gets slammed by ATI's midrange offerings, costs more, and doesn't have DirectX 9.0 capability. Regular 9700's are available from $60 more than the 9500 Pro, making it a steal.
Step up to DDR400 or DDR433 ram. It'll last you past the current generation and gives more overclocking headroom.
The M-Audio Revolution has no dedicated DSP for 3dsound and relies on the host cpu to do its processing - not a good choice for gaming. Either the Audigy or Fortissimo III are fine choices. Remember, only Creative cards have EAX HD support, but as of this time, none of the games that utilize it are worth buying. You can bet that Doom 3 make extensive use of it though.
The rest of your choices are good ones though. The 2Ghz XP 2400+ will outperform the 1.83Ghz 2500+ Barton when you up its FSB to 333mhz and has more overclocking potential. The 5% boost from the extra L2 doesn't compensate for the lack of clockspeed when there's front-side bus parity.
That said, within the next two months Intel and AMD will ramp up their bus speeds sending current motherboards into obsolescence, and new videocards from ATI and Nvidia will shakeup prices all the way down the scale. If you've waited this long, what's another 1 1/2 months right?
