So you might've come up against a little bit of a brick wall trying to get information regarding your trusty Kensington Expert Mouse in relation to Windows Vista. Specifically I was irritated that the scroll-wheel wasn't working. Here's a quick fix that doesn't require installing MouseWorks (specifically because Kensington seems to be hinting that we shouldn't do that on our Vista machines):
1. Download the latest Win2K/XP version of MouseWorks (6.22) and unzip it to a folder (copy the path from the automatic unzipping utility *before* you unzip) and click "OK"
2. Open up Control Panel -> Mouse -> Hardware -> Properties and click "Change Settings"
3. On the Driver tab click "Update Driver..."
4. When it asks, click "Browse my computer for driver software"
5. Paste the path into the "Search for driver software in this location:" text box and ensure that "Include subfolders" is checked.
6. Next, etc. and you're done. Now use that scroll-wheel!
Note: This doesn't seem to help with buttons 3 and 4.