The only problem with logging into your AP would be if you are using a separate DHCP server, or if any users have static IP addresses.
If you have a separate DHCP server you should check that instead of the AP.

If anyone has static IPs, then I would probably go with Nmap (which is available for Windows) or some other IP/port scanner.
You could also use something like Kismet or the aircrack-ng suite to find out who is actively on your WLAN.