Why would you want Windows 98 when you have XP and plenty of space?
Why would you waste time with OS/2 3? If you really love that OS, then put it by itself on another box.
Yes you can share swap space between Linuxen.
Don't waste your time with Debian. MHO of course.
80 Windows on NTFS, 256M swap, 79 Linux. Since the disk is so enormous you don't need r/w access to the Windows partition. You can mount NTFS r/o.