Neighbor keeps inserting his wireless router into my network infrastructure?

If someone hacked into your router, they could well have hacked into your computer also and you may have something running in your computer that is doing this.  Its very hard to diagnose over this forum.  But if you are losing bandwidth, it suggests hacking.  And that is illegal and it might be used for illegal purposes, so if you knew it was someone hacking, you can contact local law enforcement, as it is more than someone accessing your internet capability (such as might be the case if you had an unsecured network).  This is robbery by tampering with your system, so that is clearly not kosher.  They could also be using your bandwidth for illegal purposes and the cops would come after you, as its your account.

I would scan your systems for malware and viruses.  Then also go to Start | Run and type msconfig and see what programs are running at startup and its possible there is a program that is resetting the "Belkin thing" or is opening a back door to your system.  For diagnostic purposes you might also try turning off the wireless features completely and just running the router hard-wired and then see if you get the "Belkin thing" coming back in. 

Its likely someone very close to you as the wireless signal doesn't transmit over the entire neighborhood.  It could even be someone in their vehicle out on the street.  If you are friendly with the neighbors, you can ask them.  Otherwise I'd ask law enforcement for their advice.

steve