Don't wig out too much A1... Alpha means they are still working on things like core code, AI, object rendering, object collisions, etc. By Beta they turn their eyes more towards compatibility, UI bugs, etc.
But to be honest, you may want to install Windows 7... Vista was SUCH a bug-filled monster...
You may even get 64-bit to work on your machine, which if it was supported, could give you greater speed and extend the life of your PC for a little while longer.
Not that that will help you with getting this to work in Alpha... just saying...