These two function calls open and close the CD tray.
Because the command "wait" is included in the command string, the function returns after the command has been executed:
uses
MMSystem;
{ open the CD tray }
mciSendString('Set cdaudio door open wait', nil, 0, 0);
{ close the CD tray }
mciSendString('Set cdaudio door closed wait', nil, 0, 0);