new to cross fire have a question or two

[Shadowmeph]

I have a cross fire motherboard what would happen if I install a 3870x2 and a 3870 can I do this and if I can is there going to be that much of improvement of running these two cards together ?

[CMetaphor]

Yes you can tri-fire a 3870x2 and a 3870. However, the older 3xxx series cards don't scale as well as newer cards (like the 5xxx series). You'll probably get a maximum of a 10-15% boost in FPS, and only at high resolution (at lower resolution you might even loose performance in tri-fire). HIH.