Yes, it's possible to extract megavideo's video urls. Just emulate what the player does.
For instance, here:
http://www.megavideo.com/?v=PDGY09BO
Check the sources and look for "<embed", you'll see "<embed src="http://www.megavideo.com/v/PDGY09BOdd25c9a8fbb2c02157e89cfe73c9dac5" type="......", there is the embed URL of the player.
If you put that URL on the browser, it will 302 redirect to "http://wwwstatic.megavideo.com/mv_player.swf?image=http://img3.megavideo.com/d/d/25c9a8fbb2c02157e89cfe73c9dac5.jpg&v=PDGY09BO", where you can clearly see in the URL the image(background image that shows on the video) and an id, named "v"(short for video would be my guess). Next the player calls this 2 URLs with the "v" id: "http://www.megavideo.com/xml/player_login.php?u=&v=PDGY09BO
" and "http://www.megavideo.com/xml/videoad.php?uid=1258325079240
". As you can see, that's login and ad information, irrelevant. Now, it loads "http://www.megavideo.com/xml/videolink.php?v=PDGY09BO&width=1680&id=1258325433624&u=", which has all the moolah you need. In that data mashup you'll find your video URL.
As for the uid/id param on the last 2 request, I'm not sure where it get's them from, you might want to decompile the flash player and check.