[G4] Perplexed need help

[Robert C. Buitron]

I have a G4 dual 1.25 GHz PowerPC, 2GB RAM (maxxed out), 4 internal HDs 
(3 SATAs & original Seagate ATA), a SIIG PCI SATA controller card 
4-channel for Mac that can boot from any attached drive, and a Sonnet 
Allegro PCI Firewire 800/1394B card. The OS is 10.5.5. I boot up (or my 
startup disk) from the original ATA HD at this time.

The problem is kernal panics and freezes.

Some additional background:
About a month ago I was downloading some Apple software updates when I 
encountered some freezes that eventually turned to a kernal issue as I 
did troubleshooting. I used the Disk Utility from the DVD install disk 
to check the startup disk, which at the time was a SATA connected to the 
controller card mentioned above. All internal disks were verified. At 
one point using the Disk Utility on the SATA startup disk, the computer 
hung up. This continued to the point that I had to power down, power up, 
heard the drives spinning but blank on my monitor- just black.

I did some internal HD troubleshooting and finally determined that it 
was the SATA startup disk that "seemed" to be the problem. I removed it 
and swapped it with the original ATA HD directly connected to the 
motherboard, and voila, my G4 was back to "normal".

Now the perplexing problem:
I was downloading the latest software updates from Apple, which included 
the latest JavaScript,iTunes8, some remote security patch (which I don't 
  use), and some other update that I cannot remember.

I started the update and walked away as I knew this would take some 
time. A half hour later I came back to a machine that had a kernal panic 
and message that I needed to power down the machine. I did and powered 
up and resumed the update with only two items remaining of the starting 
4. I walked away again as it was iTunes 8 and JavaScript. When I 
returned I had another kernal issue but without the power down message.

The first few lines of the kernal issue are:
"System failure: cpu=1; code=00000001 (Corrupt Stack)
backtrace terminated- frame not mapped or invalid: 0x4AD8FF10
Unresolved kernal trap."

I'm not computer savvy, just enough to sometimes help myself and of 
course sometimes to create problems. Any ideas, suggestions, notions, 
preventive measures would help.

The machine is up and running. I decided not to continue with the 
software download. Seems that that was one of the contributing factors.

Thanks for your help.
Rob