Ok, I have never gone so far for hacking streams. The "usual" way for me, in win XP is to "fish" the streamed file out of opera browser cache (8.xx works great, 9.xx file is locked, 10.xx some restrictions).
1. start the video in the browser
2. pause or mute
3. drag the cache file over mplayer

Being a linux noob myself even if I'd find the streaming cache file (no idea where to even start looking for it) I suspect it might be locked.

I usually avoid clipnabber on my pc since it's an online service that can be down or even banned, and it requires the page source... Too much work when I can simply drag a file from opera cache.

On the other hand the clipnabber way is somewhat easier on N900 than browsing through a lot of files, opening terminal and finally starting the video...

But provided we would know the cache location, an xterminal shortcut could be made to directly start a rooted xterm in the cache folder with the command to list the largest files first.
Finding the video stream is easy since cache files rarely have above 500kb.

Then the only thing you would need to do would be to apply the ip, user agent and header tricks into the browser. I suspect a complicated html crafted by professionals could overcome the header issue...