Recently the computer was upgraded to Vista.
On purpose? Why? Just a tip... Forget Vista ever existed. It was all just a nightmare. Either stick with XP or go to Win7.
After installing VS2005 and all pages, pressing the RUN button throws an error where the start page is "forbidden".
Sounds like a huge shift you made without checking it out first. May I suggest that you get VMware? You can have virtual machines running on your one computer, and debug directly into those virtual machines. So you can be running Windows7 on your computer. Have a virtual Windows XP running within that, and Visual Studio can send your project to debug inside that virtual XP and still get all the debug information. It's great to be able to debug in 5 different O.S. without needing 5 physical PCs, or without needing to actually install Visual Studio into 5 machines.
May I suggest turning off the UAC? Then move the entire project out of your personal folder. Visual Studio by default saves in your personal folder. I never do it. I keep a directory at C:\Code for all my projects. Short path doesn't get hit now and then with "path too long", and I know this directory isn't being treated special, like a user's home directory does.