Kernel Panic when booting external USB drive (WD Essential 250GB)

Question

Greetings...I recently was tasked with setting up three bootable external volumes for a co-worker, so I purchased a Western Digital Essential 250 GB drive.
Everything worked just fine on my end, I was able to boot into each of the three external volumes continually and then shipped the drive to my co-worker, who when he tries to boot into any of the three drives gets a kernel panic.
We are using different models of MacBookPro (15 in. 2.16 Ghz Intel Core 2 Duo) for me and MacBookPro (15 in., 2.2 Ghz dual-processor Intel) for him. We THINK it might have to do with a firmware mismatch from the two machines:
Mine:
Boot ROM Version: MBP22.00A5.B07
SMC Version: 1.12f5
His:
Boot ROM Version: MBP31.0070.B07
SMC Version: 1.16f8
...but we've never had these types of problems before, even with mismatched hardware. The OS and kernel versions (10.4.11, Darwin 8.11.1) we're running are identical, according to ASP.
The only other weird thing is his panic log registers a different kernel version than what ASP reports, though that might be normal since hardware is not my thing:
Kernel version:
Darwin Kernel Version 8.9.1: Thu Feb 22 20:55:00 PST 2007; root:xnu-792.18.15~1/RELEASE_I386
In short, if anyone has any ideas how we can get these drives to boot or can confirm that it is impossible with the mismatched firmware so we can move forward with a plan B, I would greatly appreciate it.

Answer 1

Yes, sort of.
I used 10.4.8 disks to install, but used the Apple Software Update to upgrade to 10.4.11 on two of the volumes. I was still able to boot with my machine after that however.
As an update, my co-worker was able to "fix" one of the drives by upgrading with some 10.4.9 disks he had. He is now able to boot from that drive. That is not an option with the two others since they are already at 10.4.11.