This would be the same as COD4 packet injecting, correct? Packet injectors are not illegal as long as you use them for testing your own security, such as THC Hydra.
Try
Nsauditor Network Security Auditor
Packetyzer
wpepro
Commview
If packets are encrypted use Cain and Abel.
Have fun
p.s. Most good packet injectors are
not free. That being said google is your friend.