Indeed, I have found some work around, yet I am still not completely satisfied:
1) You can use "-vo x11 -zoom" - full screen will be working flawlessly (at least as far as I can tell - didn't test ist all that much). Unfortunately x11 will consume more performance than xv which will cause the fan the run while watching dvds. (BTW -vo gl2 works for me too, but consumes even more performance)
2) Searching mplayer mailing lists I found a post that suggested the use of -vo xvidix. Unfortunately this did not at all work (for me) - seems to me like go 5200 is not supported yet.
3) Currently my -mplayer/config contains the following lines:
Obviously this won't be quite "full"screen since it will leave 10 columns of the desktop on the right hand side, however xv will run quite flawlessly ("quite" because in very bright areas there is still the chance of seeing some glitches)
hope this helps