suggestions on how to get back to xp after installing vista

>
> since upgrading to vista beta 2 i have had a lot of problems running
> everything, when i start my comp i get a dual boot screen for windows
> vista
> and an earlier version, if i select the earlier version of windows it goes
> to
> a black screen and thats about it.
> On top of this i run a couple of cad programs which now either won't run
> at
> all or crash after opening. can anyone suggest anything to help or tell me
> how to get back to xp as i need to get on with my work
>
>
> vista does look cool thou