Triple BOot

I have 3 partitions, an NTFS for XP Mce, (C),98gb, an HFS partiton thatt is 20gb, (os x x86), and a fat32 partition with no OS, (S), 30gb.

Whenever i boot the PC, Darwin 8 asks me to boot to: hda 0, (ntfs), hda1, (os x tiger), or hda5, (fat32).
I want to leave it as FAT32 and install Windows 2000 as a back up installation and i need 2000 for certain apps.
WOuld installing 2000 erase my boot set up?

You should be able to install it so long as you select the right partition to install it onto.
However they do recommend that OS's are installed in chronological order, XP may get a bit tetchy if you install 2000 after XP has already been put onto the system.

If you need to, change the boot sequence with the 'Edit' option in the Advanced> Startup and Recovery function within the system properties.