The router is running 128-bit WEP (not all the devices connected support WPA). And is set to only allow the 3 MAC addresses I want to connect to it. Nothing else is connected that shouldn't have been.

All I know is when I download something on my laptop it gets more bandwidth with the QoS on than when off. Bandwidth tests show I'm getting about 2.4 Mbit/s with QoS and 1.9 without.