I usually say what R Proffitt said; there are plenty of USB wifi adapters that work instantly out-of-the-box in Ubuntu (a quick search on Amazon will show you a number of them) and if you shop around you can get one for under $10.
However, I did find these details: http://www.grailbox.com/2012/05/installing-cisco-linksys-ae2500-wireless-adapter-in-linux/
Ignore the "Download the latest Ndiswrapper and compile it" step - instead, just install Ndiswrapper from Ubuntu Software Center. Of course, you should be using one of the latest Ubuntus. Probably 12.10 would be better as it would have a later version of Ndiswrapper.
I've actually never used Ndiswrapper because I've always either been lucky to have a fully-supported device, or I've done the research before buying to determine that the device I'm buying will work. Long story short, I can't provide any additional support on how to use Ndiswrapper, sorry.
I put Ubuntu on an old computer of mine but can't connect to WiFi. I'm using a Linksys Cisco AE2500 USB adapter. I need help with driver and I'm not to good with configuration commands in the terminal. Help me!