You already have the programme with XP - you can use Movie Maker 2 (which can be found, assuming you have a "default" installation, Start>all programmes>Accessories>Windows Movie maker).
It does depend so some extent what you want to do with the finished product. MM2 doesn't support burning to DVD. What I have done in the past, is complete the movie, save to the HD as an .avi file and then encode and burn to DVD (or SVCD) using burning s/ware.
HTH and if you want more advice about using MM2, post back and I'll try to help.