I have my own computer business that specializes in supporting small businesses. Here is what I recommend to them:

1. [link=http://toolbar.google.com]Google toolbar[/link] - stops most pop-ups.
2. Custom hosts file. [link=http://www.everythingisnt.com/hosts.html]One version here.[/link] This blocks most ads on webpages. Add additional entries to the bottom (like utopia.rcuniverse.com)
3. Antivirus and firewall. For ease of use, I generally recommend Norton Internet Security, but there are some good free ones also.
4. Spyware removal tools. Adaware and Spybot-Search & Destroy. I tend to use both. Adaware first, then uninstall and run Spybot.

Hope this helps you as you surf the net.