Well, after browsing to "C:\Program Files\Altiris\Altiris Agent\Agents\Deployment\Task Handler\bootwiz\Platforms\Winpe2\x86\Drivers" on my Altiris server and observer that the folder was empty, I decided to restore the Drivers folder from backup. I did the same for the x64 folder, which was also empty. I then recreated all of my preboot environments. No change. At this point, I feel PXE is completely hosed.
I've tried creating new preboot environments, but nothing seems to be happening. I can see that Bootwiz.exe is running in Task Manager, but I don't see any changes happening at C:\Program Files\Altiris\Altiris Agent\Agents\Deployment\Task Handler\SBS\Images. I've hit Update on my SMA, it's been at least two hours. Nothing's working here. :-(
I've called support. Hopefully they aren't going to dismiss me outright for running an "unsupported" procedure. I'm about at my wit's end with this product. Getting very close to abandoning it for DS6.9.