Discovering hidden information on your PC

KermitJunior writes: I was recently approached by a colleague at work who seems to think that his wife might be cheating on him or engaging in otherwise "not quite right" behavior. He has asked me to investigate his computer and find any "pictures, movies, emails, browser history, bank accounts, etc." that might clue him in to a "second identity." Aside from the standard file searches and poking around settings, does anyone in the slashdot crowd know of any free forensic software out there that might help in the search? (Like recovering deleted cache, etc?) The computer is running Win98, I think. I can slave to linux, too, if that will assist.