No you shouldn't have to uninstall\reinstall them at all. As long as we're just talking about both cards being regular old PCI cards, and we're not referring to your PCI-E graphics card swapping anywhere you can.
Just shut down the computer, flick the power switch at the back of thre computer (should be a little 1/0 switch on the PSU next to the power cable), but make sure you leave the machine plugged in physically with the cable. If you flick the switch on the PSU to off and leave it plugged in, the PC will essentially ground itself to help prevent against any possible electric shock you may cause to the system. Then open up the case, touch something metale (ie. the steel case itself) and then go ahead and switch the cards to w/e PCI slot you want to.
That was probably more explanation than you needed, but its always better to be safe than sorry when messing with internal PC components... I've done my fair share of damage to a laptop or two without proper grounding.