Read what is scary at http://forums.cnet.com/5208-6132_102-0.html?threadID=119247
So while you can scrub and clean files (I think CCLEANER from download.com is nice) if you read the first link here's the brutal truth. Windows goes to inordinate lengths to store useful information in the most arcane places. If there is a lesson here if there is something you don't want to leak from your PC you replace the drive or at least start over with DBAN (do not complain to me if you use that!)
So in short, read this is scary, clean out the stuff you find then create a NEW ADMIN ACCOUNT for the new owner. Then log in there to delete the old account PLUS delete the old user home directory. You're pretty clean at this point but run the THIS IS SCARY tool again and CCLEANER one last time.
I want to pass my dell dimension 5100 to adult son. I would like to free up or erase, over write personnal files( my mom may have left old bank info?). Can I, if possible, do it w/o 'breaking' anything. I would like to have it be in its optimal condition for him. Is a reinstall of the os from the dell disk I have, the way to go? If so, what about SP 3 and all the updates I have on it? I dont have the drivers disk but have dell drivers download list on this newer dell pc. The dimension 5100 has been improved w/ wireless microsoft kb and mouse, planar flatsceen and recently installed 'avanquest fix-it utilitiles 9 pro'. It is win xp media center, 2.8 gig ram 512 2 cds; cd/dvd /rw, and 122g out of 144 of free space right now. It's a fine machine. I hope you have some advice to keep it that way b4 letting go to his hands.