If you're looking to trigger VoiceAttack commands by pressing a button on your joystick, you can assign up to two joystick devices that VoiceAttack will monitor directly(see the "Joystick Options" section of VoiceAttackHelp.pdf; Pages 102 and 103).
When you've assigned at least one joystick, you can set up command(s) to be triggered(VoiceAttackHelp.pdf pages 21 and 22) when you press a given button(combination).