internet not working, a mysterious network showing up

[Alpha]

Hi, I'm not sure exactly why but occasionally my internet (I use Airport via a SMC router attached to a PC in another room) stops working. I'm using Safari on OS Tiger. It's only happened once before today, and after several non successful tries using the 'network diagnostics' it worked again. And then it worked perfectly since, until today when several times in the span of a few hours it stopped working. The first time it happened today, my screen said I had no connection. I tried to fix this in network diagnostics, but when I tried to select the SMC router, it said "cannot connect" (this was after it prompted for a network password, and I entered all the ones I use but it didn't work, and I DON'T EVEN REMEMBER EVER SETTING A NETWORK PASSWORD WHEN I SET UP THE ROUTER - AND IT'S ONLY BEEN ABOUT A MONTH SINCE I DID IT SO I WOULD REMEMBER). I clicked 'use interference robustness' in my airport menu and then it seemed to work.

The next few times, the internet was supposedly working but either the page never loaded, or it would say 'cannot find [insert url address here] server'. And after a long while, I'd try to load that page again and it did. And meanwhile, I clicked on the Airport in the menu bar, and where it usually lists the networks "SMC" and "Other", a THIRD network, dlink, is showing - AND WE ONLY HAVE ONE SMC ROUTER IN THE HOUSE. I'm assuming someone else on our street has a dlink? We do live in a townhouse....

Now I just want to ask, is it possible that this dlink router, wherever it is, is interfering and causing my internet to be slower/not loading pages/not finding servers? What can I do about it? Could there be anything else interfering, even though my internet's worked perfectly before in the present setup and placement of the router and furniture etc etc? And what about when I had no connection and it wouldn't let me connect to my SMC router? Why did that happen?