High ping when router introduced to network

[mr_sack]

An issue from one of my friends:

I just recently moved and got a new cable modem for my time warner road runner. We have the 10 Mb/s down 500 kb/s up package. I am also switching to wireless. Now when playing games, my ping is never lower than 500. This happens with the wired and wireless connections. when the modem is connected to the computer directly, there is the normal 50 ish ping. I previously used the wireless router (although i have reset it since) for online gaming with regular performance. I remember not doing anything special when setting it up previously to get it to work with games.

I feel like this means there is some sort of conflict between the router and the cable modem.

Things i have tried:
-setting up one computer in a DMZ
-changing the MTU (although i was just guessing about appropriate values)
-using a different router

I cannot set up port forwarding since me and my roomates plan on using it to play the same games.

Thanks in advanced for the help.

 

[riser]

Update drivers or revert drivers for the wireless card. Update firmware on the wireless device (router/access point).

Change MTU to around 1400 on the PC and on the Router/wireless. There are two settings for it.. not just the one on the wireless device.