MSDN has a Vista developer story series on how to develop applications for Windows Vista.

http://msdn.microsoft.com/windowsvista/downloads/docs/developerstory/default.aspx

One of the particularly useful articles is on Application Compatibility

http://msdn.microsoft.com/windowsvista/downloads/docs/developerstory/default.aspx?pull=/library/en-us/dnlong/html/AppComp.asp

(also at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnlong/html/AppComp.asp)

It details many of the changes in Vista and how to change your application to comply with the Vista paradigm.

Definitely worth a read.