Hi This is a low cost way
http://ww1.microchip.com/downloads/e...Doc/51757a.pdf
The board is available for about 40 uk pounds from
www.farnell.com in the uk
Order Code: 1676254
or
newark.com
order code 07P9512 $55
It has windows sniffer software supplied and the ability to setup filters etc.
I havn't tried it but it looks like it will do the job.
Peter