Help, after installing XP over Vista, Windows XP freezes on loading screen in boot up?

Hi. I followed an on line tutorial on how to install Windows XP over Vista but now I can't load Windows XP because it freezes on the Windows XP loading screen. When I load in Safe mode it freezes on the driver called mup.sys. I have an Acer Aspire 3680 and I have all of the XP drivers on a CD. I am able to get into Safe Mode but not safe mode with networking (it just freezes on mup.sys). I would appreciate any help you can give.