Instructions
Download and unzip "No$GBA Converter" (see References) to its own folder on your hard drive. Double-click the No$GBA Converter and select "Configure." Select the No$GBA directory, or whichever directory has your VBA saves, then click "Save Config."
Select the VBA or SAV file on the next screen, then click "Convert." Press "Refresh," if this file doesn't appear right away, or if you move a file to the No$GBA folder while the program is open. In the "Save As" slot, use the .GAM extension instead of .SAV.
Click "Convert File" to convert the file to .GAM. You'll need to use a program such as Gameshark or Action Replay to add the .GAM save file to an SD card to run on a DS.