I had the same issue when I first installed Vegas 5, so I emailed their support people and got a reply (that worked!) literally within minutes!
Here's the guts of the email:
1) Open the Shuttle Control Panel
2) Select Vegas 4 as you Application Setting
3) Select Options -> Create New Settings -> Copy Contents from Current Setting
4) A new dialog box will then open. Find the executable file for Vegas 5, select it, and select Open
You now have a setting for Vegas 5. Feel free to rename the setting to whatever you choose and modify any of the buttons or wheels that don't perform to your liking. When you start Vegas 5, it will use the setting you just created.
Hope this helps you.