Wireless suggestions needed

I have a Dell inspiron 1525, and mostly use broadband. It works great and is not a problem.

The problem is when there is no service, and I need to use WiFi.  As long as I am in the same room as the router it works fine.   25 feet from the source( in an RV park for example) , I get a "poor" 1 bar signal, and none at all farther away.  The problem is on my end, as I can pull out an older Dell computer where I have 'poor" reception on the 1525, but have "excellent" reception on the other computer, even picking up additional networks. Should I assume the problem is in the card, and replace it?   Is there an external card for it that would work even better?   Any other ideas?