Some things to think about and do before installing Visual Studio 2005 SP1.

First off, a requirement:

• If you have installed the Web Application Project type from the MS downloads, you must uninstall it before installing the service pack. (Apparently the pack includes it)
  

Post is here - talks about the following:

• disable patch cache (save 1.3 GB of disk space and lots of I/O time during install)
  
• uninstall c++ if you're not using it
• will have to reinstall after upgrade to Vista