If Linux only works in FAT 32, (I dont know if it does or not, sorry), then I would be tempted to have all the drive in FAT 32.
Theres nothing worse than being in one OS and not being able to use what you want from another partition that the OS cant "see"
I would probably split into 3 as a 20 gig partition for XP, 10 gig for Linux and the remaining bit, up to around 90 gig.
Unfortunately XP cant format over 32 gig in FAT 32.
You would have to use FDISK to make and format your partitions prior to installing XP as even though you could get XP to format the 20 and the 10 gig partitions in FAT 32 it wouldnt do the rest in it unless you split it into chunks under 32 gig which wouldnt reall be worthwhile