usb flash drive really slow when my wireless adsl modem/router is connected

Hi, 

I have an Inspiron 8600 (1.7Ghz, 1GB Ram, in-built truemobile b/g wireless........)

I have just recently connected to wireless broadband and find that my USB port is now very slow when using a usb (2.0) flash drive.

All I have done was add a wireless Adsl modem router.

Could this be because there is now more data going through my USB ports

Any ideas's ?

also, Is there any utility that I can use to check data transfer rate? on the usb port

thanks

css_jay99