Originally Posted by Josem
if your motherboard and your graphics card have the same manufacturer it should be possible
Don't the NB and the PCI-E slot share the lanes?
Do onboard GPUs have crossfire/sli, wat?
Google revealed that there is in fact one single dedicated card you can use in combination because it's the same GPU as you got onboard as a discrete version, Radeon 5450.
It's called "hybrid-crossfire"
Intel's quick sync engine on sandy bridge won't work with a card in the PCI-E slot and the onboard GPU will be deactivated.
On the other side, in win7 you could use a nvidia and AMD discrete GPU at the same time.
Drivers/software are able to support all that, just the circumcised onboard GPU don't.