If you have 2 IDE channels, and one CD drive as well:
IDE1: Master: 15GB drive (with OS on)
Slave: 30GB with games/software
IDE2: Master: 40GB with swap file, mostly backup stuff or MP3's and stuff.
Slave: CD/DVD drive
This is assuming all the drives are the same speed (although the 15GB will probably be slower)
If it is, make the fastest drive the OS drive, and the swap file on seperate channel.
You could partition the fastest with about 10gigs for Win 2k and essential apps, so it gets less clogged up.