crossfire-faqs

I am not sure if those older cards support crossfire.

http://game.amd.com/us-en/content/images/crossfirex/CF_...

This link does not even have them on the table. So i would say no.

If they did support it, it would be CrossFireX which you need a special VGA cable in order to use. Your motherboard would have to support CrossFireX.

I dont know if mixing a X1600 and an X1650 would even work yet alone different RAM capacities.