Capturing simultaneous keypresses

I'm trying to write a game but I can't find a function which allows multiple keypresses at the same time, eg. moving and shooting at the same time using spacebar and arrow keys. Right now I'm using ProcessCmdKey which only allows one key at a time. What function can I use?

PJ

http://vbforums.com/showthread.php?s=&threadid=280308

This example is in visual basic, but it's the principal you're after, not the actual code.

Bill