Pocket DVD Studio ($39) certifies Windows Mobile 5 compatibility.
If you still have the compression program you speak of, you could use that and play the video in
TCPMP (The Core Pocket Media Player, $0).
I used
DVD to Pocket PC with my X30 and it worked great, but have not tried it with my X51v. Many more exist. Check
PocketGear and
Handango for other options.