You should keep your Windows based computer up-to-date via the Windows Update Service on the web.
In addition, there are online sites that help with PC maintenance such as PC Pitstop.
For other misc programs, there is a great freeware program called FileHippo Update Checker that will check for updates for Adobe Reader, Java, Quicktime, Flash, Real Player, and many other programs. You may also want to install Secunia PSI to check for outdated and insecure programs installed on your computer.
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Ten Steps to Troublefree Computing