I recently bought a new computer build with an asus m4a78- pro which supports hybrid cross fire the onboard is a 3200 and I'm just wondering if there is a way to run it in crossfire with my 4850?
No. Generally you should disable the onboard video if you're going going to use a 4850 and the onboard video doesn't disable itself automatically, as 780G boards can, upon detecting a card other than what it can Hybrid Crossfire with.
It should tell you in the mobo manual if it can handle hybrid crossfire, and--if it can--how you go about enabling it. I don't know how much of a performance boost you will get from Hybrid Xfire, but your manual will tell you if it can be done.