|according to Micro$oft, WinXP 64bit OS needs a minimum partition of 6Gb. you may be pushing your luck there.|
what you could do is get a FREE d/l of partitioning software as was mentioned above viz >>> GPartedLiveCD and reduce the size of your current HDD partition IF you have enough free space at the moment (assuming that your 40Gb HDD has only one partition), keeping in mind that your present OS needs at least 15% of Free Space to perform routine maintenance tasks viz >>> defragging.
the simplest method would be to do as aegis suggests above and get another HDD and install winXP64 on that and anything else you want. you could then just simply "dual-boot" either HDD from within BIOS Boot Tab, without actually setting up a "dual-boot" with a Boot Manager.
you have hardware driver support for WinXP64bit ?
EDIT: you need more RAM. 1GB is bare minimum with XP64
Central Coast NSW Aussie
There are 10 types of people in this world: those who understand binary and those who don't.