Don't know why re-running would change your network settings, as far as I know it shouldn't. A few more questions:
Do you have any other DHCP servers on your network?
Have you made ANY changes to DHCP settings in lmce? I know of at least one bug in b3 where changing your DHCP range (ie from 192.168.80.x to 192.168.0.x) will cause it to not function.
I wouldn't think either of these could be the issue since it works fine when you PXE boot. Actually, now that I re-read your first post, after you PXE boot to a MD can you browse the internet from it?
After you boot XP open a cmd window and run ipconfig /all and post that here.