speed is noticably slower? Not sure why this is happening.

I'm using the Linksys Wireless-G Broadband Router which is connected to the Modem and the main computer. I'm using a Wireless-G USB Network Adapter on the new computer to pick up the internet from the W-G B Router.

The new computer with the USB Adapter picks up the internet, yet the internet connection is much slower than the main computer...

Any thoughts, ideas or suggestions?

Thanks in advance,