@blakespot
yes, the 128-bit memory bus is important for reasonable performance, but, again, the main contributor to poor video playback with some files is the CPU itself. that said, a 128-bit card will help. if you can't find one on ebay, let me know -- i think i have a spare 9250 somewhere.
as for overlay, it should 'just work' without any setup on your part. there is a NOOVERLAY tooltype for dvplayer that you can enable, but unless you did so, it's on. it's a shame i'm up in CT, or i could diagnose all this in person. can you tell me the file container and codecs used (video and audio) of the file that is stuttering? maybe can i help you cook up the right settings to play it well on mplayer.
-- eliyahu