3 Monitors, 2 through Graphics Card, 1 through Onboard from Mobo ?

I have an asus crossfire II mobo and asus 9800gt graphics card with 2 monitors attatched to it but want to connect my 3rd monitor, will my pc get messed up if i connect the 3rd monitor to the onboard graphics on the mobo ???

Calling all Experts – Please Help !!!
Many Thanks in advance!

PS i have windows 7 ultimate 64bit with 8gb DDR2 800 Mhz ram, if that helps