I've been looking everywhere to find out more information about this problem but I haven't been able to (not even Google could answer my questions this time). You know how when you hold down too many keys on your keyboard it gets angry and beeps at you? Basically the system I want to use in my games has the possiblility of the player pressing up to 5 keys at once. Sometimes this isn't a problem and the input is received fine, but depending on what keys I press it doesn't take the input. For example, when I hold 5, 7 and 8 on the numpad, it will beep. When I hold 5, 7, and 9 there is no problem. I'm baffled as to why this is. It would seem that if it can handle having 3 keys pressed then it should work for any 3 keys, not just certain combinations. Is this a Windows specific thing or is it related to the keyboard hardware?

This is a problem with the keyboard hardware itself. This article explains it pretty well and has a link to a more detailed article about it.

Thank you, this is exactly the kind of thing I was hoping to find!