I have a similar problem here. It could be one of a few things:
1) your browser. You don't mention what you're using, but I use Mozilla here in the office. I can't see Youtuube videos without taking certain actions. With my Microsoft Internet Explorer, however, I have no problem.
2) If you're using Firefox as I do at home, you shouldn't be having the problem UNLESS you don't have the latest FLASH plugin. You can get it here:
http://xrl.us/bhjoc
3) Always check to be sure you don't have malware running on your PC. In SAFE MODE, do your scans. You can do this by pressing the F5 or F8 key while starting up your computer or by typing MSCONFIG in the START button's RUN command (XP or higher only).
4) As I mentioned in another thread, P2P processes can also be interfering with your download time. Also, if you share your connection on a network then traffic from other computers thru your router might be the problem.
I've never used Unubtu so I can't address that.
Anyway, let us know what you find out.
Good luck.