Limit Bandwidth Using WRT54gs

Set up:
Actiontec M1000 - running in DMZ mode pointing to wireless router
WRT54GS Version 7.2.06 (wireless router with 4 ports)
6 Meg DSL Connection

Issue: Computer connecting via wireless router running program that requires port forwarding. This program runs between 500 - 700 kbs. When this program is running at these speeds the speeds of other computers is running at anywhere from .03 megs to .6 megs. I cannot install any third party software on the computer running the program that needs forwarded ports. I also cannot install any hardware on the network.

This is what I have tried to so far:

Accessing the WRT54GS Config page I selected QoS. The computers that I am most worried about with the low speed test are hard wired. I have selected Ethernet Port Priority for ports 1 and 2 (mine and my girlfriends computer) I set the Priority to high for both port one and two. We are the only one's hardlined from this router. Everyone else is wireless. I also enabled flow control for these two ports. I have also changed the device priority allowing for highest priority for our mac addresses. There is no difference in our speeds while hardlined and our devices listed in Device Priority. I have also listed the port in the Application Priority and set it to low. Speeds of hardlined computers are still unchanged. It seems that with the WRT54GS these settings are just psychological.

I am not the owner of the network, I just maintain it. Also the owner knows enough...prolly more than me. Yet, I am wondering how to maximize the bandwidth of the two hardlined computers while still enabling the owners program to run at it current speeds. I am also baffled that with a 6 meg connection, the program only uses .5859MB of the 6 meg capacity according to http://www.t1shopper.com/cgi-bin/calculate.pl. Any assistance would be greatly appreciate thank you for your assistance in advance fellow geeks.