Well, not enough power would flow. Your video card may not start, but your system fans could spin. Or your whole system doesn't power up. Nothing serious happens when there isn't enough juice.
I'd test it first to see if the system powers up. If it doesn't, then get a new PSU. I somehow doubt the 8600GT will draw 22 amps on the main +12V rail. Does either of your PSUs have mutli rails? (2-4 +12Vs)
|TG-13th| Acreo Aeneas Former 9th IHS Member
I am NOT an acorn! -.-
Give it a shot. I really don't think anything bad happens to the hardware when it doesn't have enough power. The worst that could happen is the system crashes. Although you probably bought a new PSU by now...