You cannot push the file from the android program itself, use the adb push command.
Create the file like this:
mksdcard 1024M sdcard1.iso
Restart the emulator using the sdcard
emulator -sdcard <filepath>
Then go to the android sdk/tools folder and push you file to the device like this:
adb push foo.txt /sdcard/foo.txt
Sometimes you need an emulator restart again.