I prefer the old DOS games from the 1990's to the modern 3D games. I discovered the GOG.COM site and purchased one of my old favorites Hocus Pocus Hocus Pocus runs well under MS-Windows 7 (64-bit). Occasionally I fumble on the keyboard and it shrinks from full-screen down to a small window. and I don't know how to put it back to full screen without killing the game and starting afresh.

My big question is: "Can I use a simple USB joystick with these old DOS games purchased from GOG.COM on a modern PC running under MS-Windows? If so, where can I buy a simple USB joystick? All I need is joystick navigation with a fire button and a jump button. instead of one ot those complex things with lots and lots of buttons and other controls.

THERE TURNED OUT TO BE NO PROBLEM. i BOUGHT A USB GAME PAD AND PLUGGED IT IN. IN THE GAME SETTINGS I SELECTED JOYSTICK AND ALL WORKED PERFECTLY!

doesn't this game support a joystick native?

Here is a way to use a joystick or emulate one (usb in your case) with dos box

http://www.dosbox.com/DOSBoxManual.html#Joystick

Hocus Pocus runs on DOSBox, and to switch between full screen and windowed mode, use Alt-Enter. I think the same is also true for games running in SCUMMVM, and quite a few more use the same key combination as a full screen toggle.

Well, it's not about the joystick itself so much as the input it provides (direct input, xinput, etc.) and if the thing you're using it for can read it all including axes. Otherwise you use software to map it to a keyboard binding profile.

So when shopping for one, see what input modes it has for your computer/programs to detect it. The software isn't so difficult to find and a good one may even come with its own.

Amazon is usually my fallback for tech supplies, but I remember talking to an Aussie friend a few years back and being amazed there isn't an Amazon Australia.

You can use most recent console controllers with the PC if you happen to have one; Xbox 360 Controllers need a Wireless Gaming Receiver while the PlayStation 3, PlayStation 4 and Wii controllers work over Bluetooth.

Failing that you'd want a controller with at least four buttons since some later DOS games started to rely on that for changing weapons etc.; most DOS games don't go beyond four buttons due to game port technical limitations.