1. Ya, it could be. I would suspect if you had a bad setting in CMOS setup, it could cause instability. An example of a bad setting would be an overclocked FSB with a 1:1 FSB:SPD ratio to RAM that cant be overclocked.
2. If it had anything to do with your CPU, it would be overheating, or improper overclocking.
3. I dont see a problem there. 512MB is plenty.
4. If you HDs are really really full, or really fragmented and cant feed data to the RAM fast enough, then that can cause instability.
6. I doubt that your vid card would cause problems while burning a CD.
7. PSU problems usually cause random reboots/shutdowns, no matter what you are doing....no freezing.
I mostly suspect overheating of your CPU. Read my guide at the top of this forum on random reboots. I know you arent rebooting, but the overheating section still applies to you