Safety-Lab Shadow IM Sniffer problem

I have no idea how this program works. I cannot find a "readme" in the directory. I've looked on the internet for how-to instructions. Nothing.
And lucky me, it doesn't work for me. I have Wincap driver installed, latest version. The only thing I can think of is that my LAN's router has a NAT firewalll, and that its wi-fi has wpa encryption.
I will continue my search for instructions, but hopefully someone who has already used this program knows his way around it. It's an NBZ on this forum, after all. :)

*edit*
It is confirmed. SIMS successfully captures my conversations on AIM. However, when I instant message using AIM on my other PC (which is in the same LAN..), the program doesn't capture any packets at all
*edit*

you are probably connected by a switch. all traffic is split at this point and sent off down the wire to the correct computer. unless you have a device you can install this program on between your internet connection and the switch it is gonna be very difficult to sniff their traffic.

you could look into arp poisoning but its complicated.

i figured as much. i can sniff packets send through wi-fi (confirmed with two laptops, one on aim and one with the sniffer). but i'll definitely look into arp spoofing. i've heard it before and never really given it much thought.