Question
Deployment Server's PXE Server requires a stable network in order to function correctly, due to the size of its automation boot image files.  Is there a possible alternative that could be used for VSAT environments or other slow link environments?

Answer

The gPXE project is such alternative, that would allow the download of a minimal PXE image from the PXE Server (over VSAT) and to start a larger Linux PE image download over http from the local server (so the pre-boot image could be a standard Altiris pre-boot for automation task, or a customer pre-boot with X-Windows or SSH for remote troubleshooting etc).

gPXE is an open source project.

The following video link is interesting but possibly lengthy (go toward the end where the demo runs if you have a chance): http://www.youtube.com/watch?v=GofOqhO6VVM.
 
You can also check their wiki: http://etherboot.org/wiki/index.php
 
The following page indicates that gPXE can download the boot image over http (so this could be used with a local gPXE Server): http://etherboot.org/wiki/appnotes/pxelinux_tftp_to_http_migration
 

Here's an extracts of interest:
 
Changes to DHCP
dhcpd.conf
          #filename "pxelinux.0";
         
          if ((exists user-class) and (option user-class = "gPXE")) {
            filename "http://192.168.0.1/gpxe/boot.php";
          } else {
           filename "undionly.kpxe";

          }

If you go to their companion site http://rom-o-matic.net you can get a build of gPXE that suits your need. Selecting PXE Loader bootstrap image with UNDI only provides a 54KiB pxe image download.  This would mean 54KiB download over tftp + config file then all other communications should be local to your http server on site. So this would totally integrate in the Altiris PXE infrastructure.
 
Note that there's still the option to burn a ROM for on-NIC replacement.

Symantec have not tested gPXE themselves, however, the theory is sound so customers should test this thoroughly themselves.