Need help, wireless networking issue.

So I have tried a range extender, I have tried a range booster router, I have tried a wireless N router which is supposed to give much more coverage. Still I'm getting very low signal from the router on most adapters I'm trying. The N router is a belkin and the adapter was a belkin N adapter and the signal dropped off very quickly with that. A couple of the laptops I'm trying to get to work work better then the N adapter with the built in antenna. One of those laptops actualy gets a pretty good signal, stays usually at 3 to 4 bars when about 100 feet away. The other one stays at about 2 bars and sometimes 1 and sometimes disconnects.

Has anyone here ever bought a wireless adapter that actually made a big improvement on the range you could receive wireless?

That seems to be the only thing that is making a diff, so I'm wondering if there is a wireless adapter, either PCMIA or USB that makes a big difference in signal stregth.

I don't know what is causing this interference but it sure is annoying.