I used to have a motorola android milestone phone and I think it was built in or it was a free app I downloaded from the store but it was like a music app where uses an online connection like wifi or data plan in my case wifi since i dont have data on my t-mobile. anyways it let me search for a an artist lets say too short, or dr dre and it basicallys searches online for that type of rap hip songs and it starts playing music one after another from those type of genre.

Does the n900 have something like this? Thanks

Use the browser. Navigate to Pandora.com. Have fun.

I am not aware of a program that works with the Internet Radio that is part of the Media Player application.