You need to insert your xp cd and do a repair install. This is what the message is telling you to do. If your pc came with xp built in, you should have received a cd as well. Insert this cd and do what your pc tells you to do. This should start a repair install but i think you will loose any files you have saved.
I would also recommend installing more RAM on your system as xp needs quite a lot. 512mb would be a lot better!
Good luck
