To activate 3D graphics you need to enable it in the video menu or system settings menu of each game that you play. If it supports it.
I don't think that your card is powerful enough for that anyway. Also, i believe that 3D is only supported by Nvidia cards at the moment,hence the 3D glasses that they are offering with their top cards.
Regarding the RAM issue.
Have you downloaded the latest driver for your card?
Also have you plugged your monitor lead into the graphics card as it sounds like it may still be using onboard graphics.
Do you have at least a 300W PSU?