First, it appears that you are running OS 10.6.8 on this iMac, which indicates you have an Intel-based iMac. This forum is for Non-Intel-Based Macs (PowerPC G3,G4,G5). You might get better help there.
That being said, no it doesn't sound normal. However, since you're that far along, I wouldn't stop the re-install at this point.
This might be a heat issue or a hardware issue. I just saw this the other day:
I don't know if this even applies to your iMac or not.
I hope some of this helps.