First of all, there is no limit to how many OS's you can put on a single hard drive. Windows OS's can only install on a primary partition, but Unix/Linux based OS's have no problem going on a logical partition. The way this works is that you use a boot partition to tell the computer which partition to boot from, and you can have it boot a primary or a logical one. On my laptop (1 HD), I have had as many as 7 different OS's on it at once. Only 1 was Windows, and the others were Linux (for testing different distros).
Now, that said, I would install XP first. XP overwrites the MBR and overlooks any Linux installations. Next install BSD, then Slack, then finally Fedora. I say Fedora last because it has the easiest menu to add multiple OS's to the boot menu. It is possible to do it in any order, but easiest to do it that way.
While you're at it, you shoudl give Gentoo a try! If you want the benefits of Linux, and "windows like" speed, that's the distro for you! If you have any questions, give me an IM (JKHunholz on AIM)...I'd be glad to help you out.