Another way to tell for sure is to use Wireshark (
www.wireshark.org) on a machine on the same HUB (not switch) and see what kind of network traffic is generated during the startup process. Look specifically for the amount of data transferred, the time delays between various steps, and so on.
Larger profiles, especially when the profiles are stored on the network server, will obviously take much longer to transfer down to the workstation. Comparing the profile sizes, therefore, should be the first step. Beyond that, though, you should look for any other anomalies, such as network packets lost (which Wireshark should display on a easy-to-identify black background) or other network-level issues which might be restricting traffic flow.
If you have two machines, one which works well and one which doesn't, it should be relatively easy to get two traces and compare them.