MTU And Xbox Live Help?

I can get live to work but only if I reset the MTU every time I turn on the 360, otherwise it won't log in anyone know how to fix it permanently? (I have a Linksys 54g router). Also GTA IV isn't being read easily by the console, it takes several tries of opening the tray and closing it, sometimes it takes as many as 30 times for the thing to read, it doesn't do this with any other game, do I need to buy another copy of GTA IV?