Do I need to say that my ex-girlfriend is stealing my mail?

I put two posts up on this forum last week trying to get some insight into a problem in which someone used my IP address to view all my e-mails (some personal, some not) and forward some of them to people they should NEVER have gone to.

How is this possible? I'd like to be able to understand the way this happens without having to devote 12 hours a day for a year or more to become a hacker/cracker. Will someone please fill me in

Also, what can I do to prevent this sort of thing in the future? The person that broke into my home computer (remotely) has created alot of havoc in my personal and professional life, and I'm a little exasperated that I can't get any help on the issue. Norton has been attentive but pretty much no help (not to mention that you can't understand half of their techs because they all seem to be in India), and my ISP is completely useless as they don't recognize that this happened.

I could really use some help folks! I thought there couldn't be a better place to find out how my security was breached than on a Security Forum, maybe I'm wrong.

Thanks.............