If you have a pre-release version of VS2005 (full or express skus) installed, then before you install the release version you must uninstall any of the prerelease software and components you had installed, and you have to do it in a certain order. If you run the VS2005 prerelease versions Uninstall app from your Add/Remove Programs applet in Windows you will get a nice notice letting you know this.
Fortunately, Microsoft has released a really nice tool that will uninstall all of the VS2005 prerelease software and components and do it in the right order for you so you can upgrade to the release version.
http://lab.msdn.microsoft.com/expressrtm/uninstall/