A couple things to note... huge maps are not as much fun as they sound anyway - seriously, make a basic max-size map in the editor, then wander it. For some clarity, the Final Fantasy 6 world map is 4128 x 4128, and the Chrono Trigger world map is 1536 x 1024. Chrono Trigger gets away with a much smaller map, for having multiple iterations of it. Final Fantasy 6's world was quite large and took a long time to explore.
As for your laptop, that 2G for the GPU is likely shared RAM, which means if the graphics card needs up to that 2G, it's taking it out of that 4G of RAM that you have. Large images take up a huge amount of RAM no matter what program you use. You may not be able to work on something so large with the machine you have.