Fan not working booted up with XP?

It might just be that your fans aren't necessary because your MacBook isn't overheating. When you are in xp, realize that you're using a very powerful machine and that the os was developed some time ago and needed far fewer resources than what you have.

While in xp, you could try opening several browser windows and run some youtube vids in each to see if you can up the heat and see if the fans eventually come on as a test.

 

Try running a game and see if the fans start kicking after 15-30 mins of gaming, then it should work! Probably doesn't need to run faster while in XP.