I actually might be able to help with this one. *SMILE*
I have a T30 with running Slackware-Current and MPlayer installed by SwareT. If I'm logged in as Root the following command gets the job done:
gmplayer -vo -xvidix
If I'm not Root that won't work because of an issue with scanning PCI slots (even if I designate the radeon driver) and so I use the following command which I believe is next best:
You might also try this command which works for me as well but is not preferred due to the fact that with this option the video is not resized along with the window. Hope this helps.
Ah yes, just so it's known, the -vo represents the "video output driver" choice and you can find out more about it in the man pages.