Traffic Shaping

I have been trying to get traffic shaping setup for my 2 computers at home without much success. I think I may have narrowed down my issue to the fact that I have very inconsistent internet speeds. I'm on a wireless microwave link and my connection can vary anywhere from 200kbps to 1500kbps. Having such a large range of variability affects my ability to set proper pipes.

Here is my basic setup.
I have two network cards setup on my Monowall box each assigning their own IP's

192.168.x.x assigns an IP address to my wireless router which then connects my own computer

192.168.1.x assigns an IP address directly to the other computer in my home.

Basically the only thing I really want to accomplish is have high priority for my World of Warcraft and Ventrilo traffic coming off of my wireless subnet. I've tried setting up many different rules and pipe wides from really small to really big to prioritizing traffic by only one IP to just the ports that WoW uses yet the other computer still continues to consume ALL of my available bandwidth when initiating a download.

Do any of you have any recommendations on how I could set this up or is this an issue of me using two seperate NIC's in the computer where the rules are not being applied across both NIC's?

My Monowall box is setup as the following:
WAN => NIC1
NIC2 => Wirless Router => My own PC that needs high WoW/Vent traffic priority
NIC3 => Desktop PC (Which needs to not interrupt my WoW/Vent pings)