NVidia, Linux, and Hardware Acceleration

When I got my Asus laptop, I immediately installed Linux Mint 9 "Isadora" GNOME and searched for the proprietary NVidia graphics driver. For some reason, at that time, nothing turned up. I didn't really worry about it, as I could enable 3D acceleration and desktop effects anyway, and they worked really well, as they still do. A few days ago, I got the idea of looking again to see if I could install those proprietary drivers, as those might give my computer using Linux Mint even greater graphics capabilities. To my pleasant surprise, this time, the drivers were found and had already been downloaded; all I needed to do was click "Activate", and I did. I then restarted the computer and logged back in, only to find that I could no longer use desktop effects. Well, that was strange. The thing is, I have 2 graphics cards in this computer (an NVidia GeForce 310M and an Intel GMA 4500); Linux Mint recognizes both (as tested in the terminal), but I don't know for sure which card is being used. Furthermore, deactivating the driver brought back desktop effects. Has anyone else had similar issues? Does anyone else know what to do in such a situation? Thanks in advance!