You may be a bit confused by the requirements (understandible.) It may be that you are saying Airport Extreme card when you actually mean Airport Utility. Airport Utility is an Apple application that can be downloaded, free. It should already be in your computer, although, it may need updating. If you purchase the Airport Express, you will get an installation disk which will walk you through the proccess of setting it up.
With regards to your computer, it has all the neccessary ingredients to work with the Airport Express and other wifi networks, including the wi fi card.
Yes, indeed -- this does include WPA2 Personal. Some very old versions of computer type devices don't have
WPA2 cabability, but they will be few and very far between. I have an Airport Express in my network to handle wireless devices that I have in my home --including an older ipod, a blu-ray player that we use to stream movies, and a bunch of guests who use smart phones ipad, i pods, all without difficulty.
The Express is a very good wi fi product, and I'm sure just about anyone on this site would advise you to use WPA2 security. So I think you're a smart cookie to go that route.