although i am not an expert but just have a little knowledge regarding your problem.
just check your cash drawer if it connected directly to a printer there's a little jack at the back near the printer port cable or somewhere depending on the model, if it has then it is included in the printer driver already. Once you click the rpint button of your form it'll automatically kick-out the drawer.(Printer that hasno problem regarding the connectivety of the drawer is EPSON, STAR.
but if your drawer has a connection for serial port of the PC, here a little code i can share to you, this is what i do, just put in a click event of your button, but dont forget the mSCOMM activex to put in your form, and you dont have to put anything at that active x.
here's the code
if it won't work just e-mail me i have small code from Vbasic for printer specially that ABS-POS printer
i hope this will help