When it's giving you trouble, open the task manager and look at the second tab, sort by CPU and see if you can determine what the troublesome process is.
Do you have any NetBIOS, Microsoft networking going? Finding shared volumes can take forever in some cases. Try going to the properties of your network interface and turning off client for Microsoft networks and file and print sharing.
I know iTunes has a sharing protocol as well. Is this turned on? I'm just speculating.
