What version of Ghost?
What boot environment (DOS, WinPE ??)?
Are you using Ghostcast server ?
Have you checked the actual connection speed of your NIC? Although it is a 100Mbps device, it can also run at 10Mbps, and this can often be determined by looking at the connection light colour on the hub/switch.
Frankly, there are so many variables, that without much more detailed information we can only guess where your problem is.