sorry, no you cant.
the closest you can get is to have two machine, A and B, and two domains 1 and 2.
connect computerA to domain1, and computerB to domain2.
now buy two more network cards, and insert one into A and the other in B.
Now get a crossover cable and connect the two computers together, and set their IPs
now share the internet connection on each computer. Make sure that the input is the netowrk domain, and output is the crossover.
After you have done the steps above, you should now be able to access both domains on both computers, without problems.
unfortantly, if domain 1 fails, this system will not keep the internet going from domain 2.
I have set this system up before, and works perfect.