You'd better believe it's possible! I'm doing exactly the same triple-boot, albeit with different partition sizes.
First thing you're going to need to do is shrink your XP partition. If your XP filesystem is FAT32, not a problem--just use fips.exe, usually located in the DOSUTILS directory of your Linux CD. (Failing that, enter FIPS.EXE as a google search, and it'll probably be your first hit). You'll have to use a boot disk to get into pure DOS in order to use FIPS, but it's semi-intuitive, so you shouldn't have any trouble shrinking your FAT32 partition.
But what's the point of using FAT32 on XP? You're probably using NTFS. XP uses NTFS 5, which FIPS doesn't grok. You'll need Boot-It NG. I've forgotten the URL, but it should take you approximately 8 seconds to find it on google, even if you're on a 14.4 modem. Unzip Boot-It NG to a directory, and have a blank floppy ready, 'cause it just copies a disk image to your floppy. It says it's shareware and will expire after 30 days, but that's only if you install it, and you only need to install it if you plan on using it as a boot manager. You're going to be using Linux, so you already have a boot manager. Just boot up using your Boot-It NG floppy. It'll throw an error saying that it doesn't have a proprietary partition for its bootloader, and throw you into the partition manager. You can nondestructively shrink your XP partition, make the remainder into an ext2 partition (or just leave it unallocated), and CTRL-ALT-DELETE.
Pop your Linux CD into the drive, let your BIOS know you want to boot from CD, and you're stylin'. I can't speak for all distros, but I know Mandrake 8.1 will accurately detect your other OS's and automatically configure LILO to boot to them. (Although it does call XP NT)