After you have downloaded and installed the SDK,
Then, open Command Prompt,
enter the directory
e.g.
android-sdk_m5-rc15_windows\tools\
android-sdk-windows-0.9_beta\tools\
Create the virtual SD card with this command
mksdcard [-l label] <size>[K|M] <file>
e.g.
mksdcard 1024M c:\sdcard.img
To add files inside the virtual SD card,
use the adb command, adb push <file> <destination>
e.g.
adb push c:\music\Android.mp3 c:\sdcard.img
Under Command Prompt, use this command to start the emulator
emulator -sdcard <file>
Once emulator is running, you can also add files using the Dalvik Debug Monitor Service (ddms) tool,
run \tools\ddms.bat
select Device > File Explorer -> SD card
Add files to the SD card by clicking the Push File from button in the toolbar
Thanks!