How can I go back to a previous boot ROM version?

Question

Hi. I've been reading these forums for a long time...first time posting.
The short story: I have a Macbook 5,2 running OS X 10.5 with boot ROM MB52.0088.B06, and I'd like to know how to flash the boot ROM version back to MB52.0088.B05.
The long story:
I have a MacBook 5,2. It came with OS X 10.5. As far as I know, the latest boot ROM for 10.5 on a Macbook 5,2 is MB52.0088.B05 (EFI 1.4) (see http://support.apple.com/kb/HT1237).
A while ago, a friend convinced me to update to 10.6. Apparently, with the 10.6 install, it updated the boot ROM version to MB52.0088.B06. Now, I'm concerned that there is a firmware issue (which I might be wrong about, and the reason I think there is a firmware problem is very convoluted but I'll explain if you want). So I decided I wanted to go back to MB52.0088.B05. I had been thinking about going back to OS X 10.5 anyway. So, I backed up my system using Time Machine to a Time Capsule via ethernet. Then I did an Erase and Install with the original 10.5 install disc that came with my Macbook. Then, I used Migration Assistant to restore most of my system from the backup. I should have taken a look at the boot ROM version before I ran Migration Assistant...but I didnt.
The boot ROM version still says MB52.0088.B06.
I tried downloading the MB52.0088.B05 update and running it anyway, and it says my computer doesn't need the update. When I was still running 10.6, I did try the method described here: http://pubmem.wordpress.com/2011/04/09/flash-efi-firmware-update-manually-on-a-m acbook-51/ (which has apparently worked for someone else on a 5,2; see https://discussions.apple.com/thread/3747472?start=0&tstart=0), and it didn't work. I don't know if it's a good idea to try it again now.
So:
Why didn't my boot ROM go back to MB52.0088.B05 after a clean 10.5 install?
Did Migration Assistant import the previous boot ROM somehow?
Should I do another clean install without MA?
Should I try PubMem's manual method again?
Is there another way I can flack back the firmware?
Thanks a ton!
P.S. I'm posting this in the Time Capsule community as well, since it might be an MA issue. Don't get mad, I'm new. If that's against the rules, I'll take it down.
Specs:
Model Name: MacBook
  Model Identifier: MacBook5,2
  Processor Name: Intel Core 2 Duo
  Processor Speed: 2.13 GHz
  Number Of Processors: 1
  Total Number Of Cores: 2
  L2 Cache: 3 MB
  Memory: 2 GB
  Bus Speed: 1.07 GHz
  Boot ROM Version: MB52.0088.B06
  SMC Version (system): 1.38f5
  System Version: Mac OS X 10.5.8 (9L31a)
  Kernel Version: Darwin 9.8.0

Answer 1

At least you have made some progress. My inkling is the optical drive is dead.
I think you're right.
To run the AHT you would need the AHT disc that came with the computer, but it's unlikely you have it for that old iBook G4.
I do have it, in fact! But it's not working. Here's the situation, copied from a conversation with Kenichi Watanabe over in iMacs...
I haven't been able to run the Apple Hardware Test. I have the AHT CD that came with the computer (v1.2), and I also downloaded v1.2.6 here and burned that to a CD. In both cases, when I load the CD into the external optical drive which is connected via a firewire cable (exactly what I used for the install disc), restart, and press and hold C, the computer ignores the CD completely and boots from the HD. Any idea how to fix this? Or, is there another function I can use to achieve the same thing, maybe in single user mode?
Regarding the Apple Hardware Test CD, holding down the C key will attempt to boot from the internal optical drive.  Since there is nothing in there, it boots from the internal hard drive.  I would try starting up with the Option key held down.  That should get you to the Startup Manager screen.  If that CD is in the external FireWire drive, it should be listed as a startup disk choice.  Select it and see if it will start up from it.
Right, that makes sense. Unfortunately, in both cases, when I select the CD to start up from, the screen blinks for a second and then returns to the screen where I am supposed to choose a startup disc. It does this as many times as I try to choose the CD, until I select the HD and start up from there.
When I put either CD in the drive, with the computer on and booted from the HD, the CD mounts, and Disk Utility says it's verified. But when I try to select it as a startup disc from system preferences, it doesn't show up. Ideas??
Update: I tried Hoja's reccommendation from this thread using Open Firmware, but in response to
     boot cd:\diags
It says:
     can't OPEN: cd:\diags
for both CDs.