Opinions - nVidia drivers kept crashing/rebooting this PC or is it bad RAM..???

Here's the scenario....

First - My PC is...
Gigabyte 7N400 m/b
AMD XP3000
1 Gb PC3200 RAM (read on)
FX5700 card
SB Live value
Win XP Pro SP1

The first drivers I used on this system with the FX5700 were the 53.06
drivers. All seemed to go well and no real problems with any games. I
install Far Cry and play it virtually all the way through. It crashed
back to the desktop just once. Hey, ok that's not too bad is it..???
I finshed the game but I decided to play it again on a harder level.
No big deal, only I try to move to a newer set of drivers as 53.06 is
painfully slow in this game. All goes well for a day or two with the
56.72 drivers,, then out of the blue, the game locks up. I have to
press reset to get it going again. Ok, I restart Far Cry and pick up
from where I left off.. No hassles, as all goes well for the rest of
the evening. Next day I play it again, only this time it locks up 4 or
5 times like the day before...

OK, 56.72 must be a bad driver for my PC so I went back to 53.06. All
is fine again,, but slow... I tried 53.04 drivers and these go better
than 53.06 but they too start locking up. Back to 53.06... Now all of
a sudden the 53.06 drivers lock up too in Far Cry.. Strange...!!! They
also locked up at the desktop a few times too and on the internet
too...

I use Ghost backup to restore an older backup and all seems to go well
for a week or so, then I decided to try yet another set of newer
drivers.. Guess what... Yes, it locks up in Far Cry again... Only now,
not only is it locking up but sometimes the PC switches itself off or
reboots by itelf and even worse, it tries to reboot but hangs during
bootup... Things are looking quite bad, but worse is to come...

I restores the same Ghost backup and things go well again. I decided
upon two actions...
1).. No nVidia updates
2).. No Far Cry
One or both of them "must" be the cause of this chaos...

OK 2 weeks go by and I buy Thief 3... By now I have played no games
for a few weeks and all seems to go well. I installed Thief 3 and
played for 3 days and nights and the lockups came back only this time
around it comes back with a vengance... It got so bad that I decided
to reinstall Windows... This I did and made several backups at various
stages before I bothered to install any nVidia drivers. I finally
installed 61.21 drivers and almost instantly the lockups began again
and real bad too. Now the PC is having troubles even starting, once
even refusing to go through the pre-boot hardware check. It stopped at
780mb of my 1Gb of RAM and froze... There was someting massively wrong
here.

I had 2x 512mb of matched RAM in Dual Channel mode and I began to
suspect this may well be a problem as it never really impressed me, as
it seemed to run quite slowly for 1Gb...

I switched the PC off and pulled out both sticks of RAM and put only
one back into slot 1 and now my PC seems to run well. I played Thief 3
for just on 6 straight hours without a single incident...

Maybe, just maybe, it has cured it. Maybe I had a bad stick of RAM.. I
now only run 512mb and it seems to run faster than the Dual Channel
1Gb that I had.... I can't figure it out... Can you..???

Here's hoping I have fixed it...

Anyone had similar problems....???