I'm new the gp2x scene, but after trying just about everything at least twice (with an R1/R4 dvd and sound synch issues) I got a good rip with VLC version 0.8.6e, and it works with the built-in player too:
CODE
"C:\Program Files\VideoLAN\VLC\vlc.exe" -vvv "dvd://D:@9"...