If by "dragging data files" you mean anything other than your own pictures, documents and movies, you are going to run into problems.
I would advise the re-install just to circumvent problems later on.
The easiest way is to boot off your XP CD (check that your BIOS is set to boot from the cd before the hard drive) and choose the option for a full install. Delete the existing partitions and create new ones (use the default settings).
Then install as usual