Keith, are you launching the game from the Steam GUI? If you haven't done this already, you may want to try locating the .exe in the Steam folder, and then create a shortcut on the desktop and run it diectly from that (this worked for me for "Shatter", since I couldn't run that darn game right from the GUI for some reason). Run it as an Admin. Also, in the Windows Task Manager, click on the Processes tab & make sure you have only one instance of Steam.exe running. Then, try setting the Priority to "high". Hope this helps.
Edit: forgot to add, have you tried verifying the integrity of the cache files?
Edit2: any weird error messages in Event Viewer?