The Developer ISO was discontinued, as none of the developers used it any longer. We all build things in a VM or jail based on the same OS as the pfSense install being worked on, and then move binaries over to the firewall.
Setup a VM for FreeBSD 7.2 and you can probably compile the driver fine there, and move over the resulting .ko file to the firewall.
If you have a driver issue, you're better off trying out 2.0 at this point to see if it behaves any better.