I'm pretty sure there isn't a way to do exactly what you're looking for. You could technically set SCCM's boot image to be one of the menu options within LANDesk PXE boot, but I'd be very surprised to find any PXE process that expects to run concurrently with another. The underlying technology is simply DHCP requests and responses, so as you mentioned, the client simply makes a request, any or all servers receiving the request answer, and whoever's answer gets to the client first wins.
Having LANDesk PXE server serve the SCCM boot file would be the way to go because you essentially should not need the use of two PXE servers. Like Mach6 said, the sole purpose of the PXE server is to serve the client a dhcp address and then transfer the boot file via TFTP.
LANDesk serves boot.wim while SCCM would serve boot2.wim. So the best route would be to modify LANDesk PXE server to serve both boot.wim and boot2.wim.
Is there something that is missing here that there is a specific reason why dual PXE servers are needed?
Agreed that the LANDesk PXE could do all the heavy lifting for both. Once you PXE boot, you should be able to choose where you want to go. The LANDesk PXE allows for a menu, where as SCCM doesn't.
I was going for dual PXE (one answers, but if there is no selection, then it rolls to the next one) because that seemed the best solution at the time.
When it didn't look like that was possible, modifying the LANDesk PXE seemed like the next best idea.
Creating that pointer to get to the SCCM WIM file is where I'm stuck.
In the original F8doc, it shows where to create a new menu item, and even how to edit newboot.1 using WInimage.
However, there is nothing in the documentation that shows how to point to a WIM file, and I don't see a WIM on the LANDesk PXE machine in the images directroy.
How do I get it to redirect?