Question : Problem: PCI vs. PCI Express

I have a vacant PCI slot.
Can i plug a PCI express card into it.
(I know that i cannot plug a PCI into an EXPRESS slot)

Answer : Problem: PCI vs. PCI Express

No. PCI Express are not compatible with standard PCI slot.

Additional feedback
http://www.geeks.com/techtips/2006/techtips-24sept06.htm