wireless NIC poor performance

I have installed Wireless NIC Linksys (USB) on Windows2000 Professional PC -Dell 4300 having 256MB RAM.
It is already configured to connect to Access point. Communication is fine.
Ping command shows <10ms while communication. But when I browse the network, it shows extremly poor response. Once I locate the resources (HDD/Printer) again it works fine. Can any one give clue how to resolve this issue?