What model of Thinkpad is it?
On the bottom of the laptop there should be a label with all kinds of info - have a look for "Model No" and post it here. I can talk you through removing the hard drive.
If you are looking to re-install XP, let me know which version of XP you have (don't need to know license key - DON'T post that on the forum!) - just the version. XP Home, XP Professional, etc. It'll be written on the green-ish microsoft label.
I can send you a copy of the right install disk - that's allowed, as long as you have the right install key. If you don't have the MS Licence key, you'll have to buy a new one.
A license key looks like
this