Just installed new OS, computer freezing... HELP!!

Question

Hey all,
So as I've been posting between here and the Panther forums recently, I belatedly upgraded my OS over the few days from the last version of Panther to the last one of Tiger, and now I've been having a frequent problem with the computer freezing.
Granted, I've had this computer crash on me before; sometimes it's with that Glazed-over grey screen & telling you that to hold down the Power button to restart it, sometimes, the mouse icon will just FREEZE up, and I'll also have to hold down the Power button. That latter type is the more common one, and though it may happen every few weeks or so, just today alone, I've had it freeze up on me FOUR TIMES. Even now, I used my old Panther boot partition--which I'd cloned to my external firewire drive--to boot up from and write this.
So I'm lead to believe it's either some problem with the new OS, or the computer itself. The thing is, this is a previously used G4, one I'd inherited from my brother, who said that it used to crash on him almost daily. He suspected it was because of either a problem with
A) the internal drive (the drive IS a 111.8 GB one, which seems a bit unusual for a boot drive; my old G4 came with a 20GB one, I haven't heard of many pre-installed internal drives being 100 GBs, though I could be wrong), or
B) 3rd party RAM that he'd had installed when he bought it, which perhaps wasn't quite as good as Mac-made RAM.
Anyway when I took it over, I made sure to reformat and zero-out the hard drive, and didn't seem to have AS many problems. However, obviously if I've upgraded to a higher OS--which of course would cause more wear on the computer--if the RAM was at all compromised before, then that would DEFINITELY be I'm having an issue now.
I verified and repaired ALL partitions before I installed this--on the 2 partitions of the internal, and my external--and they seemed to come up okay. I'm just like to try trouble-shooting--whether I need to run some tests, or make sense of the Crash Log(s)--on what could not only CONTINUE to be causing to this computer to crash, but have made it worse.
Admittedly I'm a computer noob, so I'm hardly the most knowledgeable person when it comes to detecting problems. Thing is, I really hope that this computer can tide me over until I upgrade to a newer PowerBook or iMac within the year, and was even going to try installing and learning some new design programs in the meantime. However, I don't want to get too comfortable with it--****, I CAN'T--or waste my time and money installing a software or a new RAM or an internal drive if there's no hope to salvage this thing.
PLEASE help! Thanks.
+_Other specifications_:+
+Machine Model: Power Mac G4+
+CPU Type: PowerPC G4 (3.3)+
+Number Of CPUs: 2+
+CPU Speed: 1.25 GHz+
+L2 Cache (per CPU): 256 KB+
+L3 Cache (per CPU): 1 MB+
+Memory: 1.25 GB+
+Bus Speed: 167 MHz+
+Boot ROM Version: 4.6.0f1+
MEMORY
DIMM0/J21:
+Size: 256 MB+
+Type: DDR SDRAM+
+Speed: PC2700U-25330+
DIMM1/J22:
+Size: 512 MB+
+Type: DDR SDRAM+
+Speed: PC2700U-25330+
DIMM2/J23:
+Size: 512 MB+
+Type: DDR SDRAM+
+Speed: PC2700U-25330+
DIMM3/J20:
+Size: Empty+
+Type: Empty+
+Speed: Empty+
+*ATA SPECIFICATIONS:*+
+ATA-6 Bus:+
+Vendor ID: 0x106b+
+Device ID: 0x0033+
+Revision ID: 0x0000+
ST3120026A:
+Capacity: 111.79 GB+
+Model: ST3120026A+
+Revision: 3.76+
+Removable Media: No+
+Detachable Drive: No+
+BSD Name: disk0+
+Protocol: ATA+
+Unit Number: 0+
+Socket Type: Internal+
+OS9 Drivers: No+

Answer 1

Nope, it'd just been the 1 "loop" (what does that even MEAN, by the way?) that had been the default when you first download and use Rember. Again, I even shut down both the display and computer "sleep" features in Energy Saver, and it ended up taking 4525 seconds, or 75 minutes.
Although "all tests passed," should I consider such a lengthy test-time as a red flag? Why would it be taking so long for such a test??
So assuming the RAM in question IS actually okay, I guess the next question is whether the computer freezing (which happened AGAIN, right before I was going to post this; Firefox was one of the only programs I had running) is due to:
A) Problems with the internal/boot drive itself (again, it IS an 111 GB drive on a G4 a used G4, I'm not sure if that's a standard factory-issue drive, and the family member who passed this computer off to me doesn't remember either). If you know of any OTHER ways to test it to make sure it's not compromised or failing (since it already seemed to come up okay on Disk Utility), I'd appreciate it.
B) Problems with the Tiger OS itself. Although the installation of it went all right, the computer DID freeze while I was doing the upgrade from 10.4 to the 10.4.11 package in Software Upgrade afterwards, so maybe that's somehow compromised the entire OS. So if there's any way to DOWNGRADE to 10.4.1, and REDO the packaged upgrade, let me know.
C) Possibility that I should still increase my RAM either way. Again, of the 4 slots, I have 2 512-pieces, 1 256, and 1 empty. So I COULD upgrade add another to the empty slot, or increase the 256 to a 512, or both. If you know of any reputable places online or elsewhere where I can buy compatible RAM for this G4, I'm all ears. I DO have some RAM on my own OLDER 2000-model G4, assuming it's even compatible (I'm sorry to say I don't know that much about RAM, never having purchased any on my own).
Any feedback or suggestions would be greatly appreciated. Thanks!