I plan on getting PC2700 512MB of Samsung and plan to overclock it. Is it necessary to get ECC? And what's "Registered" and "Non Registered"? Thanks for any help.
ECC is not needed for the typical home user. It does error-checking, but it slightly slower and not necessary.
Registered memory slows down the RAM by one clock cycle. This helps with stability under certain conditions. Not all motherboards can use registered, and registered and unbuffered (non-registered) are not interchangeable.