Re: vista installation location. I think you should be fine running as your user, ... but Blizzard specifically install WOW to somewhere in C:\Users\Public\ to work around Vista permission problems with C:\Program Files...

Take a screenshot in WoW and see if you can find the .jpg in your file system. If you can find the screenshot where you expect it to be, everything should be fine.

I still think dodgy ram is your problem. Windows is a stable product (3rd party drivers aside), if you are having freeze touble it usually is the hardware in my experience.