All of what he said, but.....
The 11Mbs you see is stepped down from the 54 you saw earlier, because there is a slower wireless connection on the network (I take it that you roommate is using a older 802.11"B" card) the wireless connection will step down to the lowest speed that ALL cards on the network can handle. Some of the newer routers can handle multiple variations in wireless speed.
That being said, that is not you issue on the slow down. Your ACTUAL internet connection is A LOT slower than your network connection. Most likely, your roommate is using a filesharing program of some sort (most likely a torrent program). Such programs uses channels to transfer (ports), you can block such ports in your router settings. Look on your roommates computer and go into the settings of the program he is using and look for ports, that is the number that you want to block. Then look in your router settings and input the number in the respected fields.
But because of you describing your roommate as "nerdy" in nature, he would just have to change which port to use, but if he's not clever enough to remember this, it can help. Also you can set it to block a RANGE of ports (like ports 2000-3000) so if he does change the numbers, he would have to be outside of the range. I would keep the lower 2000 ports opened and then see what port the programs that you use utilize and work around those numbers.
any more questions just ask
oh and also, if the router gives you the option to backup the settings, DO IT, after you have everything the way you like it. You never know if your roommate might "happen to hit the reset" on the router Also change the password on the router.