EyeTV version 2.3 added a Front Row-esque full screen menu against a black backdrop, and then EyeTV 2.3.1 made it more unique with active moving backgrounds. I liked the original black theme better, so I had a look around and found that the new menu is actually a Quartz Composer document.
If you want to change how it looks, make sure Quartz Composer from the Tiger Developer Tools is installed, and find your EyeTV application in Finder. Control-click on it and choose Show Package Contents from the pop-up menu, then navigate into Contents -> Resources and open FSMenuBackground.qtz in Quartz Composer. There is also FSMenuBackground.qtz, which appears for 'One moment please' and 'No signal' messages. You should restart EyeTV to see the results of your changes. You should, of course, make backups before changing these files.
Don't get too fancy editing these, because it seems the composition is running constantly in the background (even when the menu is not displayed). I noticed this when I added my iSight to the background and the iSight's light didn't go off.

