About a year ago I had to employ a registry hack to get a certain game working (The Witcher, pretty cool RPG).

I don't remember the exact hack but I know it had to do with VC80.dll or something like that. It also involved side-by-side configuration.

The problem was the game was looking for a certain version number, which was wrong (loads of people were experiencing this problem), so basically I had to change the version number in a few spots in the registry.

Ok in the process I made Windows unable to use Windows Installer, which means I can't install a ton of useful programs and updates of preexisting programs.

I have tried to retrace my steps from memory but I can't seem to do it. What is the best way of restoring my registry to where it was a year ago without losing too much subsequently acquired data?

Also I do not have Vista disks. I have an Hp Pavilion m8150n. To be honest I'm not sure where my copy of Vista is within my PC. I guess in the recovery drive or something? But I don't know how to access that.

Sorry for being so mega-noob. I'm really not dumb just not very immersed in the inner-workings of PCs.