FYI: Picasa2 is a photo editing program and will do nothing for the security of your PC. Firefox is a browser.
We all get spam, it is just a factor of modern technology, but you can do things to reduce it. Search in Google for "reduce spam" and see if any sites help.
Here is one I found:
http://www.us-cert.gov/cas/tips/ST04-007.html
You ask about changing your email address, but it sometimes help to have TWO email addresses.
Have one for just your family and friends. NEVER give it to anyone else, NEVER use it on the feeback forms, NEVER use it to register for web sites.
That email should stay fairly safe from spam.
Use the other email for everything else and just accept you are going to get spam.
Some email programs do have a junk mail filter that can filter out spam and junk mail, but none of them are 100% accurate because the spammers use different technology to get round the junk mail filters.
They rarely use the same email address to send out mail, and often misspell words like viagra to get round the filters.