I see this is a bit of an old thread, but thought I'd chime in. With Risen right around the corner I wanted to load up and play a bit of G1 and G2. I have a machine running Vista 32 bit ultimate version.
I have no problems running G1 straight out of the box.
G2 (Gold version with NotR expansion) is a weird beast however. After I install G2 I can run and play the game. No problems. However, after I've shut down my machine and later turn my PC back on, I can no longer get past the Disc check.
I also happen to have a disc copy of Gothic Universe which also includes G2 + NotR. Same result. I can play the game fine right after install. But as soon as I turn off my computer and later come back, turn it on, and try to launch G2, I can't get past the disc check.
And yes, each time, I have the disc (and the CORRECT disc) in my CD Drive.
Like txa1625, I downloaded G2 from GoG and everything works fine. I like the freedom of not having to have the disc in the drive as well, it's very nice.