Using MAC numbers is a DLink choice....several items in the logs would be much more readable if they had used IP addy's instead.
What you need is to keep a listing of your MACs as they relate to IPs so you can do a quick reference and see if some other MAC is showing up.
MAC filtering will usually do this for you, but it can be hacked, or rather spoofed by somebody who knows their stuff. If you are in fear of such a person on your LAN, you should be using WPA2 wireless encryption (with AES cipher) to begin with... This is also how you work towards the promised land of 300 Mbps wireless anyhow...