Can i Crossfire my X1950Pro with a HD3870?

I don't think even Hybrid Crossfire will allow that much of a difference, though I'm not totally sure. I think it was meant to be same card, different clock speeds or something.

Dx 10 and dx 9 cards, could be some conflict there...

If running in DX10 mode yes, but in DX9 mode that conflict wouldn't exist. I really don't think it will work, perhaps a HD3850 and HD3870 would though. Still, it's worth a shot.

Has anyone tried it already? Or should i email ATI and see what their response is?

I was under the impression that you needed a Crossfire master with the X1900 series. That might prevent Crossfire from working between generations.

even if you did do it, i'm not sure you'd gain much more from the 38xx over a 2x1900. the 38xx would have to slow down to match the 1900.

i could be wrong..i don't know much about dual card setups.

Usually crossfire only works with cards that have the same GPU. A 3870 and a 3850 will work (same Chip). A 1950 and a 3850 won't.