In my LinuxPE, I modify the netconfig file; only initialize the interface on which PXE image was received.
To do that, locate your netconfig-file, it should be in
\pxe\masterimages\menuoption130\BDC\shared\etc\netconfig.
In that file, change or add:
INTERFACE=$ALTIRIS_PXE_INTERFACE
That's it; let me know if it helps.