I've got the stock wooden grips off and I'm trying to put on the rubber grips. However, there is a rollpin at the base of the grip frame. Should I remove the rollpin to install the new grips?
I don't see how the new grips will slide over the rollpin to install otherwise.
if those are fullsize hogue rubber grips, you need to use the rollpin to hold the adapter included with the grips. then screw in through the bottom into the adapter. the grips will fit over the pin.
Do what Pote said, you might be able to look inside the rubber grips and see a track-like grove that the rollpin (with the adapter attached) to slide down into. You might need to jiggle them around a bit until you get the hole lined up wth the adapter hole that the screw goes into. Shouldn't be too difficult to do once you get it started.