he he he. That is called "dual booting". A lot of people do that.
Do realize that when you install XP, it will erase the MBR, therefore the bootloader will be gone. I'm not sure how Linspire does their rescue thing to reinstall the bootloader but you will need to find out before you put XP on there. Each distro sort of has their own way of doing that.
You may be better off to just wipe out the drive completely, install XP, then reinstall Linspire. Sort of get off to a clean new start. May have to since windoze really likes to be the first partition on the first drive anyway.
Hope that help and gives you a little BUMP.