This was taken from gigabyte.com about my particular motherboard.
Experience the advanced ATI Hybrid Graphics Technology, which is including ATI Hybrid CrossFireX™, ATI SurroundView™, and ATI PowerPlay™ with Windows Vista and XP* supported. With combination of onboard GPU and a single VGA card’s GPU*, ATI Hybrid CrossFireX™ can bring remarkable display performance on AMD platform, and also further to increase your overall system value. ATI SurroundView™ allows 4 or more monitors support at once and also ATI PowerPlay™ enables power saving profiles to help reduce power consumption and further resulting in reduced system temperatures and fan noise.
* For Windows® XP, please must install AMD Chipset driver version 8.51 or later.
** Please use ATI Hybrid CrossFireX certified VGA card (i.e., ATI Radeon HD 2400, 3400 series).
Does this mean it will work in crossfire with my current 4870? The onbaord graphics it says is a 4200.
No, only the 2400 and 3400 series can crossfire with the integrated AMD 780G.
This thread has many links outlining ATIs "plans" of Hybrid CrossFireX, plans that have yet to be implemented if not already completely abandoned. Even if your 4200 IGP had hybrid then only the low end 4300, 4400 and/or 4500 series would be able to use it.