Go windows/one linux and use parallels or vmware to run the rest. With that kind of space its gonna get painful do to a tri boot. with the overhead that many distros and windows has, by the time you get done installing all of them, you will probably have 7-10 GB only to use per OS.
At least that will allow you to move off the unused vm and save it on an external drive or whatnot if you dont plan to use it for a bit.
But as for an idea if I were to do it ....
Using win2K (not xp, eats up too much space) and Debian and Ubuntu:
hda1 win2K 15GB
hda2 / (etx3,deb) 10GB
hda3 / (ext3,sarge)10GB
hda5 /mnt/data (ext3 or something of the sort that can be shared across all OS's. Yes windows can do reiser and ext) 24GB
hda6 swap 1GB
Give or take that would work well for the time being. Remember one os is much easier to manage. You would be best off using whatever primary OS you want and going VM for the rest. My mac and desktop are like that and its a hella lot easier to use every distro. Parallels is $50 for a dual lic, win+lin key.