It's a bit fiddly to use gpm copy & paste in Links, but yes, you can do it.
The trick is to use your key (with left-click+drag) to select the text you want to copy.
Then you need to click in the field where you want to paste, and use +Middle-Click to paste.
My (Debian squeeze) console has been a bit weird lately (I sometimes need to press a key several times for it to register) but I managed to get it to work after a few tries.
Bear in mind that links sort of behaves a little bit like vi in that there is a separate text entry mode that you have to activate to tell links that you want to enter text. If you mouse-click on a field, (or press enter on it if you've navigated to it via arrow keys) that activates it.
