New to Win7 - networking problems

I have 4 computers in the house, all networked. 2 running XP, 1 running Win7 starter (netbook) and the last wunning Win7 Pro (desktop). Problem is that I can't see the netbook on the network from the Win7 Pro machine. I can see vice versa.....and access shared resources from the desktop from the netbook no sweat. The XP machines used to be able to network to the Win7 machine, but now do not...