How many OSes are you using?
If you just have one OS and the 75GXP is your only hard drive use 2 (one for OS install/apps/games and one for MP3s/files you don't want to lose in a format, the split is up to you. I'd do about 18/12, I have about 7 gig of MP3s, so if you have more or less you probably want a different split).
If you have one OS and a second hard drive just make the 75GXP one partition (use the 2nd hard drive for MP3s/files)
You have to re-install all your apps and games if you re-install windows anyways (unless you want to do registry mucking) so there's not much point in putting it on separate partitions.
If you have more than one OS it's a little harder to decide, I also have a 75GXP, here's my setup:
I dual boot Win98Se, Win2k and Linux.
IBM75GXP 30Gig:
1Gig Primary: Win98SE install and boot.
10Meg Primary: Linux /boot (this guy is probably uneeded since my Linux main is inside the first 1024 cylinders anyways, but if it weren't you'd need this)
2Gig Primary: Linux /
24.9Gig Extended:
1/2Gig Logical: Windows swap
2.4Gig Logical: Win2000 Install
1/2Gig Logical: Linux Swap
About 6.5Gig Logical: Windows Apps (I install stuff for Win98SE and Win2k to the same drive so I don't duplicate files, but each OS needs it's own registry so you have install stuff you want in both twice, I install drivers and OS specific stuff so the appropriate install partition)
About 15Gig Logical: Games.
(that only adds up to ~28gig, but 30gig advertised is 27.9real gigs)
I have a second hard drive, 17 (15.8) gig fujitsu
It has a 14gig Windows "files" drive. MP3s, downloads, documents, stuff I don't want to delete in a format.
i has a 1.8Gig Linux /home partition for the same reason, but of course Linux can read FAT32 so it can get at all my MP3s and stuff on my Windows "files" drive. there are a few things I like to keep on an Ext2 partition though.
Install Win98SE first.
Then Install Win2k and it will configure a boot menu for Win98SE and Win2000.
Then add Linux to the Win2k boot menu, this is very easy, if you have a book called "Linux in a Nutshell" it tells you how to add it (it tells you for WinNT4, but the process is exactly the same), or if you don't have that book look for a post by SUOrangeMan, and in his Sig he has a link to a thread he wrote on this topic, it's quite well written.
Edit: oh yeah, all of my Windows 98SE and 2000 partitions are all FAT32, I didn't feel that I needed the features offered by NTFS for my system. The Linux partitions are of course Linux's native FS, Ext2.