Hmm, strange. I don't use Vista so I can't really comment on if ATI's Vista drivers work properly.
As for changing your settings, check out ATI Tray Tools. I'm not sure if it supports Vista (I haven't used it in at least a year), but it's worth a try.
*edit*
ATT's page says for the latest version, 1.3.6.1042:
[*] Added support for Vista 32bit. Not all of functions will work under Vista at this time.