Registered or non-registered ram for 12 yr old server

Hello,
I have a Dell Power Edge 1300/500 server. currently the machine has 1 slot of 256 ram. I need to buy 3 more sticks for a max of 1 GB. The problem I am having is that I am given two options ... non-registered or registered. I tried ran CPU-Z which caused my server to freeze up 3 times. I called Dell and they asked for the service tag and I gave them every number on it and I was told that none of the numbers are service tag numbers. So I decided just to buy 4 new sticks . The Dell man said Registered is better, the other salesman said non-registered is better. I read that the registered takes longer but is more stable, but I also read that you should never put registered ram in a server not designed for it. Any and all help appreciated. Thanks<
Laura