Windows XP? Yuck...
Wipe it and re-install. A Solid State Drive would be a worthy improvement, but you may not get the best results because the OS and hardware won't support all the features of the SSD.
I would suggest reading both of these write-ups:
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How to optimise Windows XP for SSD
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SSD Tweak Guide
But definitely a fresh install. Who knows what the hell is installed on it.