Nigel, your post could not have come at a better time.
We have a highly customized Initial Deployment job that leverages lots of DOS comands (choice.com, find, etc). Our PXE boot process has been working great for many years until we received a Latitude E6320.
First we booted into PXE after receiving the laptop to deploy the base image. We ESC'd out of the PXE boot process, ran RDeploy and were off to hunt for the appropriate drivers. Having put together our driver package, we put the system into the build process to see how it would work.
We used RDeploy to begin with and kept getting "Out of Memory" errors immediately after rdeployt.exe started to roll the image.
The Altiris DS console showed "Rdeploy: Internal error: assert failed." and occasionally we received an RDLog "Memory allocation failed. Not enough conventional RAM for the ream mode disk i/o buffer."
Out of ideas, we swapped the RDeploy image for a Ghost image and received the error message which is the subject of this post "Could not allocate page table memory" which consequently led us here.
We could run ghost.exe and rdeploy after having exited the PXE boot process but if the Altiris DS was managing the RDeploy or Ghost image deployment the process would fail with memory errors. The solution was simple and took 5 minutes.
We grabbed HIMEMX.EXE from the link in Nigel's post, dropped the file into our PXE configuration (we put it in the folder where config.sys is), edited config.sys (DEVICE=\HIMEMX.EXE), saved the configuration, restarted the build process with the E6320 and everything worked perfectly.
Thanks Nigel