I'm new to pda's and I'm looking for one that can support MPEG-4 video. Like the TH55 and TJ37 clie's for the price and the WIFI. Checked out the UX 40-50, and like those too, but price holding me back and 40 only has bluetooth. If you have a better choice let me know. I am also on a Mac and PC, if that matters to ya.
There are a few variations on MPEG4, such as DIVX and Quicktime. The TH55 natively supports the Quicktime MPEG4 format with Sony's included Movie Player.
MMPlayer is a good 3rd party software solution that supports MPEG4 too: http://www.mmplayer.com/