Because you are using Ubuntu 9.04, which is derived from Debian (and therefore uses .deb executables), your option was .deb for Ubuntu 8.04+ (the plus means 'and above')
Sometimes this does not work so there is another thing you can do but 2 ways of doing it. Try the link via You Tube first to see if it works. (If it does not there will be no harm what so ever!)
1) Applications -> Accessories -> Terminal
type this exactly (you can cut and paste or highlight it (USUALLY - this is Yahoo!) and click your mouse scroll wheel)
sudo apt-get install ubuntu-restricted-extras
[you will be asked for your password. BTW when you are read carefully to see if it is your user or root password being asked for!!] *********final thing:- if you use kubuntu then replace ubuntu in the 'command' I gave you to type so no cutting and pasting there. The same applies to Xubuntu!!)
2) System -> Administration -> Synaptic Package Manager
IN the search box type restricted-extras and look down the list for ubuntu-restricted-extras (or xubuntu or kubuntu !!!!!) click ON the box to the left. Choose install (or whatever it says) Now you can Click on the big green tick (check) and away you go. (if it asks you (or when it does) if it can install a list of other crap, say yes. This other stuff is the (very safe) extras like codecs for mp3's etc and flash for You Tube.
Got it?
Great cos I'm abed.
Night
email me with anything so long as it is in more than 6 hours
i love ubuntu