I'm using PIII 450 with 384 MB ram, but you should be fine with 128 for N-Track (I work for a computer company, we've got ram coming out our ears
Definitely go with 2000 - it was lightyears better then 98... make sure you get the latest and greatest version of the Delta drivers, not the ones that come with the card. Get the latest (stable) version of n-track (I haven't tried the beta yet)
As I said, having the LIVE function is nice (I can show my fiancee what she would sound like with reverb, etc using it) but I often just use the patchbay to flip to monitoring the inputs while recording, then flip back to wavouts when I've got everything in.
I haven't done THAT much with things yet, but so far it is working great (other then the level problems I'm having (see other thread)). The nice thing about LIVE is that you can monitor new stuff + old stuff at the same time when overdubbing. Most of the time doing that has worked fine, but I had to play with the ASIO settings until I found one that didn't pop but still sounded realtime (low is better, but too low will pop)
N-Track is not a RAM hog like some of the other programs out there. Personally, I liked Vegas better (I evaluated it) as far as interface, but I didn't like it $300 better - especially since Vegas doesn't do VST.