dlehrner,
Unfortunately, one of the limitations of the PXE protocol is that it's basically impossible to network boot from an ISO file like you would a floppy disk image. It stinks. :(
In the Linux world, you would typically load your kernel and initial ram disk via PXE and then mount your file system over NFS (or similar). There are a few sneaky ways around this. The parted magic project,
http://partedmagic.com/, sends the / file system (squashfs) over tftp and it runs from RAM. Perhaps you can figure out how to create a squashfs from your ISO - I've never looked into it.
The next obstacle you're going to run into is that the old 3com bootstrap pretty much limits you to only booting DOS. Here's my rant on how to migrate over to using pxelinux as the bootstrap.
https://www-secure.symantec.com/connect/forums/one-pxe-menu-unite-them-all-dos-linux-winpe
I agree w/ Randall; checkout gdisk. It's really easy to create a couple disk images and append whatever commands you need to the autoexec.bat file.
Good luck,
-B