If it runs stable without any freezes, booted from the installer CD, then the problem is evidently internal. (Call me Sherlock.)
I’d check all wiring and connections between the HD and the mobo AND between the mobo and the PSU. Might be a scraped wire or short somewhere in those pathways. In essence, make certain everything is tight and solidly connected. (Including video and any other cards present.) But shouldn't be any other cards until you get it to boot dependably and repeatedly.
Then there’s always the cleaning of RAM connections on the sticks themselves / as there have been lots of problems attributed to tarnished... oxidized, or otherwise "dirty" connections there lately.
Also, what other PCI cards might you have inside / installed within that machine? Disconnect and or remove everything not immediately necessary for basic operating function including external drives, USB sticks or other items /devices.
Bare necessities only.
Normally, when experiencing a freeze right after boot (here) there’s usually something (like an ATI extension) that’ll cause a freeze that can be worked around via the Command+Option-ESC key sequence. BUT, you were able to startup with all extensions off (and you got
that notification) and it still froze?
And finally… using an Apple mouse and keyboard? Or what?
AND... any jumpers on that HD?