Wireless connection

I just bought a MAC PowerBook with MAC OSX thru an auction and am trying to connect to the INternet. It does not have an Airport card so I bought a wireless unit that plugs into the USB port. I can get the wireless to connect to my Linksys router and get a strong signal. But when I open Safari, it says I do not have internet connection and when I try to trouble shoot it I'm either told that it can only help with direct ethernet connection or Airport card OR it locks up and says I have to restart the system, which starts the whole process over.
Any thoughts?
I am a complete novice with MACs, but have extensive experience with Windows.
Thanks in advance
Jack

Oh dear if it doesn't have AirPort it must be incredibly old.

For the USB WiFi you need special drivers, that means going to the makers web site and finding the driver for that model of Mac. Because Macs have had built in WiFi since ~2003 this may be an issue.

I think you're right. It is a pretty old one.
I did get the drivers with the wireless unit, and it seems to connect to the wireless ok. It says I have a strong signal, but Safari doesn't recognize itl

Safari doesn't decide which network to use. Either the Mac is on the net or not.

Check in the System Preference > Network does the device show up there?