Are you sure your DSL modem doesn't have a built in router? Also could your computer somehow have built-in Wireless card? If so it looks like your picking up other people's computers. (Most likely your neighbors.)
To check this out, open up a command prompt :
In the command prompt window type:
ip config /all
press enter key
look at the assigned ip addresses and see if you have more than one.
That's all I can think of at the moment.
The only real problem that I have with being an I.T. Tech is that I can't use the excuse:
"Sorry, I don't do windows."