Wireless chat monitoring

Hello. I'm not sure if this is the correct place to ask, so please direct me elsewhere if needed.

Here is my situation:

I have three PC's in my home, all running WinXP Pro/SP3.

My PC is hooked up (via ethernet cable) to a 4-port ATT modem/router.

The two other PC's in my house connect to my ATT modem/router through a built-in WIFI in one, and a USB WIFI adapter on the other.

My father's intuition (and my wife's) seem to think our 13-year-old maybe chatting with someone much older than she is, and putting bad ideas into her head. We don't want to outright confront her because she might do something stupid to rebel for interfering with her life.

Anyway. She's smart and pretty PC-savvy, so I wouldn't put it past her to check for spyware if we try to install something on her system to monitor her activity. So, the other option I saw online was Ming Chat Monitor, where supposedly you can monitor and log chats, e-mails, websites, etc. I downloaded and installed the trial, but it's not working. While I can see everyone (all three PC's) on the modem/router within the Ming program, the only real activity (websites, chats, IM, etc) I'm able to see is what's happening on my PC. With the other two, I get bandwidth activity spikes (showing internet activity), but nothing else. No packets send/received or anything.

I've contacted Ming support and they said it should work. They also suggested I try Ming Network Monitor. Still the same results. The tech guy e-mailed and said something about putting in an ADSL modem or hub, but I don't quite understand what difference that will make.

IMO, it seems the WIFI signals can't be captured/transferred through my PC for whatever reason. So, my question is, is what I'm trying to do (and what Ming has said should work) actually possible? Or is grabbing WIFI signals to my system impossible? I don't know if I have to feed the telephone (internet) line into my computer first, then go out to the modem/router...

Any help is greatly appreciated.