System: Mac OS X

I downloaded DOSBox mainly because I wanted to be able to play Theme Hospital again, which I downloaded numerous times off the internet.

All downloads failed to be recognised by the DOSBox system, but I was probably doing it all wrong, because I am technologically inept. Completely.
But anyway, I managed to get one working, and it loads and starts up fine, but I'm having problems with both the size of the screen and the mouse.

The first problem is that the screen stays the size of the originally DosBox that comes up with you load it. Any way to make it bigger? I'm on a mac, so assumed the only way to enlarge a screen was to drag it by the bottom right-hand corner (which you cannot do with the Theme Hospital screen), or click the green '+' mark in the top left-hand corner, but on the TH screen, there isn't one. Does anyone know anyway I can enlarge it, or does the DOSBox system just run the games like this?

My main problem however, is that the cursor will only move to certain parts of the screen, before the original mouse cursor appears underneath the game, so on my main desktop (obviously, as the game won't fill the screen, just sits in the middle). Is there any way to stop the mouse from doing this? It means I can't play, as some times it won't reach the icons necessary to play across the bottom of the screen before popping up on my desktop, just under the game...

Sorry if I haven't explained this properly. I just really want to play and I'm not entirely sure what to do about it. I'm assuming it's a DOSBox problem? But hell, it could just as well be God's doing for all I know about it.

Thanks so much for your help!