The size of the virtual SD card entered when creating a new AVD is the size of M that you set yourself.

And you want to put something in the SD card, looking for Android? SDk tools folder (on the command line), run

ADB? Push? XXX 1？ XXX2

Where XXX 1 is the directory of your computer (the path of the file you want to put into the SD card of your computer).

XXX2 is the directory of your AVD (just put it in /sdcard/xxx).