Nokia E71 Networking MTU Help?

I just bought a Nokia E71 smartphone and I am using Joikuspot to link my laptop to the phone's internet. So far so good, the internet works fine for the laptop, but when I connect my xbox 360 to my laptop and try to get on live, I get an error on the final step(actually connecting to xbox live). The resulting message says I need to alter my MTU settings on my router(phone). How do I do this? Any help is more than appreciated.