I have installed Vista ultimate and Avast as AVirus, it did always work perfectly with XP, but Vista keeps sending messages of conflict. The Vista upgrade test, did not advise of any conflict, are there some new drivers available for Vista Ultimate? Thanks 
avast! works just fine with Vista.
What is the exact build of avast! you have installed?
What exactly do the “conflict” messages say?
Are you using any other security program (antivirus, firewall, etc.)?