The other demo is for Crash Time 3. Honestly, how that game ever made it past Crash Time 1 is a mystery we will never solve. The demo is available in European regions only. You can add either demo to your 360 download queue by clicking the links below.
Shortcut: Download the Guitar Hero: Van Helen demo [Via Xbox.com]
Shortcut: Download the Crash Time 3 demo (Europe only) [Via Xbox.com]