Running WSS v3 and / or MOSS 2007? Go get these security rollups (security bulletin ms07-059) and apply them to your boxes ASAP... everyone should do this!
Thankfully my poetic buddy Shane has written up a good how-to post with the instructions on how you should go about updating your machines. If you've got WSS v3, just get the first patch (there's an x86 and x64 version). If you have MOSS 2007, install the WSS patch and then the MOSS patch. Shane's post has all the info you need.
If you're a bonehead like me and you install MOSS only, run the config wizard and realize you forgot the WSS one, then install the WSS one and try to install MOSS again, only to have your entire environment go belly up (yes, my entire environment was dead, no Central Admin, no sites... ugh... a horrible feeling), do the following: rerun the config wizard. The second time it fixed me up. Whew!