Is there any way to keylog my own PC?

My wife changed her password to her MSN email address after I saw something sketchy on her Facebook. She has a history of disloyalty, so I know she's resorted to emailing whoever it is she's been talking to. Is there any way to track what gets typed where? I know I can't just reset her password without her knowing, for obvious reasons. My dad, who is a retired IT wizard, once told me that every single button you push gets logged somewhere in the computer, so how would I access something like that? Thanks.