Hi Ken,
The Project 2007 SDK includes two impersonation examples. The documentation describes a simpler console application example and the code is included. It can also be found online at:
http://msdn.microsoft.com/en-us/library/aa974413.aspxI strongly recommend that you look at the online version first because is allows people who have discovered and solved problems the hard way to add "community content" at the bottom of the article.
You are still going to need the SDK. If you haven't done so already, download and install it on your development system.
Be warned that for most people getting through the "impersonation knot hole" the first time is a aggravating (a safe understatement) experience. If you are working with Project Server automation it is an essential skill. Just be patient and don't give up.
Bob Segrest, PMP
MCITP, Microsoft Project Blackbelt