If your computer isn't upto running XP then I would suggest you just formatted your harddrive and start from scratch with SE or ME. I havn't had much experience with either operating system so can't really say which is the best. If you REALLY don't wan't to format and need to dual-boot them, then I'm afraid I can't help. All my sual-booting experience comes from trying to dual boot linux with XP on the same hard-drive. Unsuccesfully I might add.
Of course, another option is to get a nice shiny new computer with XP :D
Sorry I couldn't be a bit more help but I know that somebody on here would help.