Did you include the Broadcom NIC driver?
If you go the the Table of Contents under the Help menu, you'll find a section on adding storage and network drivers. I haven't found anything (yet) that I can't talk to after installing the appropriate driver.
BartPE, like WinPE, is just a minimal subset of WinXP (or W2k3). You have to install the drivers during the build process for the hardware you'll be running PE on.