I have an absolute bastard of a problem with my network. My wife is able to connect to my pc via crossover cable and transfer files back and forth and my best mate is able to hook up and transfer files also. But I can't access there PC'c at all. I can access my Xbox no worries. But not other pc's.
Go to network settings and compair what they have that you don't. Notice the top two boxs that happen to be unchecked on my machine. You need the top two checked for yours.