just wondering if it works can they be crossfired..... or would one hold back the other

I have seen this done but cannot remember where. I think it was just after the release of the 3870. CCC saw them as 2 2900xt's. I don't think they worked very well though.

there's a chart on ati's web site of what cards will go together, well, there used to be... i think they have to be in the same family... so like a 2600xt and 2900xt... or 3870 with a 3850... not sure... i'll be sure to post the link if i come across it though

What you ment is not "same family", but same chip. 2600XT and 2900xt are different chips though. The same is true for 2900xt and 3850, even though the latter is mostly just a shrink of the XT.

Since we're talking about breeding different animals can one crossfire cards with different memort sizes? Ie; hd 3850 256 with hd 3850 512 and can one CF cards from different brands ie; MSI and HIS? Also can a hd350 be paired with a hd3870?

i tried doing an HD2900XT and a X1950PRO. It hindered the performance because it seems that it was using the PRO's horsepower while ignoring the HD's capabilities. I was hoping for some physx but all i got is half the price of the XT.

It works as long as both cards have the same chip. You could crossfire a MSI hd 3870 512 with a ASUS hd 3850 256 or two 3850s with different memory sizes. You have to remember that all cards in crossfire will revert to the slowest component involved. Using different memory sizes will make both cards use the smaller size.

At least that is what AMD propagates. How well it all works is another story. I would use google to find tests/benchmarks/reviews before linking different cards (with the same chip) together. Well, actually i would NEVER link together two cards with different memory sizes or clock speeds as i consider it a waste of money. Why not get two of the same?

Why waste the 3870s performance?

Yes it has been done, I'll try and find the article