I've found that downloading iPhone versions of iPlayer content (using this method) then converting them from h.264 into XviD works amazingly on the tablet. 480x272, so not too bad, and I think the original video is something like 384kbps, so 500-600kbps in XviD does the trick. Mplayer really seems to struggle, which I find odd, but it's perfect with the default media player. Of course, those of you outside the UK, are scuppered