Well, if you know linux you can "easily" set up a linux router and run the iproute2 tools and do traffic shaping on your cable modem's interface. It would be pretty trivial to limit everything at X speed (which is say 10% less than your sustained measured upstream) and then write a rule to filter UDP and give it 100% of your available bandwidth and give it a higher priority.
Check out the linux advanced routing howto at
http://www.lartc.org. It's honestly pretty easy to do now if you have some knowledge of linux and a strange urge to monitor your traffic levels at home.
Gaidin
Edit: I know I pimp this solution out all the time but it has pretty much been a life saver for my home network for years now. Another option to try would be netlimiter at
http://www.netlimiter.com. It's a shareware Windows app that would let you prioritize your game server over other processes but it won't let you control the rest of the traffic on your LAN.