Actually this is a tip for every computer, whether you use Wi-Fi or not, but we see the issue a lot. People will be experiencing very slow web-browsing. Sometimes this has nothing to do with the Internet or the Wi-Fi system, it has to do with their computer being full of viruses or spyware and adware. It's especially problematic in a Wi-Fi network because one person's computer, if infected with the right virus, can be flooding the network with activity and slow EVERYONE down.
Just because you have a virus protection program installed doesn't mean you are protected. New viruses are being created on a daily basis, you must update your virus definitions at least weekly in order to be protected. You must also update your windows operating system. Microsoft finds security holes all the time and they issue 'patches'. It is your responsibility to download and apply those patches before the Internet's evil-doers exploit the holes and send viruses to your computer. The latest problem is Spyware and Adware. We recommend you run both Spybot Search and Destroy AND Lavasoft's Adaware weekly to control this problem. Jim teaches a system he calls BUCS: Backup, Update, Cleanup and Scan.

1/31/05 Update: Here's a 'Frequently Asked Questions' document you can download and print about keeping your computer safe and secure. Also, here's more information on Spyware combatting programs - especially Microsoft's new 'Anti-Spyware' (now called 'Defender' - 9/2006).

For more detailed 'how-to' information I have a couple suggestions. My favorite Internet Newsletter "The Internet Tourbus" covers similar territory with lots of links in this Tourbus article . The Tourbus is wonderful because it is written for non-technical types. If you want to get a little more technical read LangaList. You might also want to sign up for this free online course Combatting Spam and Spyware. I take a lot of the CNET courses. They're great.