What exactly is the difference? I know that the bandwidth is wider on PCIe 2.0 but are there any other key differences?
Also, if you plug in a PCIe 2.0 graphics card into a motherboard with only a PCIe slot, what will happen? Does the performance of the card suffer? Are it's graphics capabilities limited or something? Or are there no setbacks whatsoever?
By PCI-E, I'm assuming you're referring to PCI-E 1.0/1.1?
A PCI-E 2.0 graphics card should work in a PCI-E 1.0/1.1 slot, with a few exceptions (although that should only be the case for certain motherboard and certain graphic card combinations, either that or that's with PCI-E 2.1 cards sorry, memory's a bit fuzzy right now) and should work without any problems. The performance of the card should not suffer, should the PCI-E 1.0/1.1 slot run at the very least x8 mode (equivalent to x4 PCI-E 2.0, which is suprisingly not much of a bottleneck for most of today's cards).