dual proc+registered memory

[oatesj77]

i'm building a dual proc machine and have a question about memeory. the board i'm looking at (asus k8n-dl w/2 single core opteron procs) uses registered memory, have to install in pairs right? my question is do i need memory for both procs? eg.. 2x512mb for proc1 and 2x512 for proc2, or can i just do 2x1or 2x2gb gb chips? i'm ordering the board this weekend, but waiting a bit on memory, i definately want 2 gb, but i think it would be better to get 2x1gb chips rather than 4x512, giving me more space to upgrade(6 total memory slots).

thanks