What is wrong with my computer and how can I fix it cheaply?

I believe my computer is infected with Spy Ware. I used an unsecured network at the airport last week and now not only is my Internet running very slowly, but when I enter a URL instead of going to that site it goes to a Google search of the site entered. I have Norton Internet Security but it hasn't picked anything up. I ran a free online program that didn't find spyware either. What can I do short of spending a ton of money to have it professionally fixed? Thanks.