Do you have children of school age or in tertiary education? Are you, or your (assumption warning!!) partner doing any night-classes, OU courses etc. or involved in education in any way?
If "yes" to any of the above you can get a properly licenced copy of XP Pro for around £75. I'll rake out an address in Stirling who will do the deed and post out the box with licence.
You could also do a search on the internet for "student licence" and "Windows XP" to see what it unearths.
Two of my boys are at university and got legal student copies of Office XP Pro for £10 each - me, jealous .... never