rooz, do you go to college or know someone who does? a lot of times, college stores offer win xp and other microsoft software (ms strikes deals with colleges and school systems, its all about product placement)
a lot of times you can get xp for $10 or $15. the copy i use is from our college store and cost only 10. and no worries, its fully legal and completely functional. on top of that, it lacks the PITA licensing in retail versions, which is a good thing. . .