Changing channels

I’ve read several topics and web sites concerning wireless. And I’ll continue to do so, to learn about securing a system. But, my head is spinning.
Still wandering around in the dark, I have a DSL modem with wireless. This I had working, using it on laptops and a wii.
I bought a D-link DIR-655 and tried to connect it (contacted tech support twice). I did get it connected using a netgear wireless usb adapter, but it repeatedly kept changing channels and dropped/connect to the signal on one of my laptops. I used the usb because it is N capable, the laptop card only has g.
So, I went to another laptop and tried to use the wireless card in it. I disable the wireless connection to the DSL modem and tried to establish a connection to the DIR-655. It did connect then the changing channels and drop/connect sequence started again.
Then I disable the connection to DIR-65 and establish the old connection to the DSL modem and now it’s doing the same drop/connect, change channels…..
Help.
Is this because I’m using two wireless units?
Or?
Any suggestions?
Jim