Renaming XP installation?

Hi guys
Apologies for asking this as I'm sure it's been dealt with before, but I couldn't find the right keywords to get answers on searching :(.

I'm in the process of clearing off a 2ndhand laptop I bought on Ebay in order to give it away - however, I've had it so long & have moved on a fair bit so no longer have the XP disc to reinstall XP on it.

What I really want to do is to remove my name from the installation (so it shows up as "BlackKats" documents, & in D&S Users etc).

I know it's linked in to the installation hence my concern - that unless I can reinstall XP afresh, I'll not be able to get it changed? I'd just prefer for the new user not to know my name as it's rather unusual & identifiable, and this is being provided as a church donation to someone in my community. It's not because I worry they'll be annoying me over any probs with it, but rather that the point is to make it an anonymous donation if that makes sense.

SO wondering if anyone's any suggestions of how to hack the Registry if required to fix this?

Thanks
Kat.