well,
it obviously depends on your price range...
a more expensive camera will deliver better results...
im not too sure on software but you can look into roborealm if you're not keen on making your own.
to move the paintball gun you will need two servos for pan/tilt and to fire it
it may require another.
look into a series of boards called "widgets", they connect through a pc's usb port
and can control servos and other things.