well i agree with all the answers but that wasnt your question, you can look in the internet history by opening a web page clicking "view" then "explorer bar" then "history" there will be a list of the sites he has visited, tho is wont log you on to anything that is password protected so not sure what you can find out from this,
she must be desperate to find out but i really dont think he will have left any traces of anything for her to find, if he is being secrtetive im sure he will know how to delete his history on the computer
well good luck anyway xxx