Suggest you back up everything and do a clean install.
You will be glad you did!
Read these tips on preparing your computer before
upgrading: http://aumha.org/win5/a/xpupgrad.htm
I would not bother. But you should defrag fairly soon after the upgrade
is complete. Before starting Read Gary Woodruff's article on upgrading
to XP at http://www.aumha.org/win5/a/xpupgrad.htm