has my computer been hacked?

From what I gather, you saw another email address in the autofill box.

I very much doubt you have been "hacked". Has anyone else used your computer?

there are a few phisching emails doing the rounds at the moment. Bes if you don't know who they are from don't open, or get a good email program that works with Outlook like, well I use Mail Washer Pro, it can check your emails for spam and you can create a friends list and a black list, plus a few more features.

http://www.firetrust.com/