How do you do this...?
 

How do you prevent people from pressing certain Keys on their keyboard using javascript?

I want to popup a URL everytime they hit (ctrl or a)

What do you mean? You can't stop people from pressing any key on their keyboard.

But I know what you mean. You can't stop them from doing certain combinations like CTRL-ALT-DEL, which is part of Windows and always wins over anything the browser does (and JS is even lower on the pecking order than the browser itself). Possibly you can do something when they ONLY hit "a" however. I'm positive nothing can be done with the control key.

Well I would like to do something when they hit (CTRL) ...

Can't.

Even if it is possible and I am not certain, but go to http://scriptlance.com and you will find out for sure, but let us say you can. If anyone wants to bypass it, all they have to do is turn off scripting in their settings anyway, so you would be better off having it made in php or cgi.

You people that have movie sites should maybe check out
The Bouncer script here... looks like it might work for you and looks like it's free.