Technically you could overclock it with a software based app like SetFSB or Clockgen (if the chipsets are supported) - but it's really, really not worth the effort.

If you are seriously trying to get more performance out of that thing - more RAM will help rather than overclocking it.

If it's just a 'because you can' and you don't care if that HP breaks type of thing - then try one of the linked apps.