I'll give it a try later tonight after work, though I don't think one can take a screenshot using Apple's DVD player. I think you can using VLC (or whatever that other DVD player app is) but don't know how the quality compares to Apple's player. I'll post later if sucessful.
I can tell you that while it looks OK, it does get kind of grainy if you're sitting close. Sitting back about 5 feet will help. Then again, the 30" display has twice the resolution of high-def TVs anyway (way more than say a 30" HDTV). You're essentially blowing up a 480 line picture to 2560x1600. Its gonna be grainy no matter what.