One bug of USB port (WinXP) with wifi USB adapter? Check if u have one plz!

I have two Linksys USB wifi adapters: WUSB11 and WUSB54G
When i try to ping my wireless router WRT54G for a few minutes (put these adapters right next to the router), i got this problem:



the latency sometimes goes very high. Ofcourse it's very annoying, especially when i play online games. I also try another router, but it's seem not to be the reason. Do u have any idea? Thanks so much!

P/s: The command for checking: Start->run->cmd
ping [Router IP] /t
For example: ping 192.168.1.1 /t