Question
How do I use WinPE* 2.1 with VMware* virtual machines?

Answer
You must use Intel E1000 network card emulation instead of AMD pcnet network card emulation. See http://www.symantec.com/connect/blogs/tweaking-vmware-work-winpe-2x-and-microsoft-vista for instructions.
Excerpts from the link:

The following works for VMware WorkStation 5.5 and 6.0 and VMware Server 1.0+. By make the following alterations, WinPE 2.x will work seamlessly with network drivers.

1. Make sure VMware is not running. Stop any virtual machines running and close VMware.
2. Browse to the Virtual machine files and open the .vmx file with your favorite text editor.
3. Add the following to the <Path to VM> .vmx file:
   
   ethernet0.virtualDev = "e1000"

   This is right after the ethernet0.present = "TRUE".

4. Save the changes.
5. Start your virtual machine.

Virtual machines with installed operating systems such as Microsoft Windows Vista or Microsoft Windows XP might have an issue with the drivers after this change. Change the network drivers and point to c:\windows\system32 for the drivers. Or download the latest e1000(Intel) driver.

VMWare ESXi 4.x

1. The e1000 NIC can be added directly (right-click the VM > Edit Settings > Add > Ethernet Adapter > select Type e1000) however the e1000 drivers may need to be installed for certain operating systems.
2. For example running ProWin32.exe located at http://downloadcenter.intel.com/detail_desc.aspx?agr=Y&DwnldID=18717 on an XP computer will load the required XP e1000 drivers. Add another Ethernet Adapter of Type = "Flexible" to download the file. The flexible ethernet adapter can be deleted when download is complete.