Update on my Vista problems
I reinstalled Vista again on my Dell 5150, but this time I used the Nvidia drivers from the http://www.nvidia.com/page/technology_vista_home.html and my lack of a login prompt has not reappeared.
However, it is not all good news, the Aero interfaces has only appeared once, the rest of the time it is the non-Aero version. The performance rating of the PC seems to vary everytime I run the tool, which might be the cause.
Anyway better than no login!