CrossfireX driver, at least an early version of it, has been leaked, and a nice gaming woman repacked it and uploaded it for you here. You will need such a driver to make two 3870 X2 to render in Quad-GPU setup. 

It is a total of 110MB download and we still have to try it to see if this is the "real McCoy."  According to some posts here (German), the user did get some performance increase, but this is a Beta driver and you should not have high expectations.

We will let you know if we get something from it, but the real stuff will be relased around Cebit; so we don’t expect much from this Beta.