WPA and Airport

My Airport card is built in to my imac. I cannot figure out how to change the network password to a WPA type instead of WEP. If I go to Airport Utility (which is where I've seen this is to be done), the utility does not find my own Airport. Will changing to a WPA help with a TIVO wireless connecting to the network?

Can your iMac See your Aiprort if you plug in directly through Ethernet?

Not sure how to do that...forgive my ignorance in this matter.

Get an Ethernet cable, plug it into both your computer and the Airport Base Station then open Airport Utility and see if the base station is listed on the left.

There is a difference between the AirPort card in your Mac and an AirPort Express/Extreme. What type of router do you have?

I don't have a separate router....do I need to get one? Everything I read earlier said that the built in Airport could transmit the signal. It does transmit. I was able to get Windows 7 on a laptop to connect when I set up a network. The TIVO wireless adapter can see my network but will not connect for some reason. So I was wondering if a WPA would be more universal. I just don't know how to switch it over to WPA. What am I missing here? Again, I apologize that I don't know much about this.

You are running what is called an Ad Hoc network. Unfortunately you cannot run WPA using this setup. Consider buying a dedicated router - the signal will probably stronger and you can run WPA.