Itunes isn't to bad as a program as a whole, however any song you by from the itunes store is protected by DRM or Digital Rights Management (or as ZDNet put it CRAP which means Content Restriction, Annulment, and Protection). Basically any song you play on itunes (from the itune store or stored on the ipod) isn't portable. Its designed to force you to play them using apple products. This is supposed to prevent people from sharing them (there is more programming involved that takes care of that part), and make RIAA and others kind of happy (not that it works) that people aren't being evil pirates.

Now to play a cd from the drive on a computer any number of players will work. Itunes (without changing anything), windows media player, winamp, etc. However these songs will stay on the cd and can't be moved.

To get something that you can play on your computer you'll need a cd ripper. This is a program that copies the cd's music tracks and encodes them into different playable formats. The most common tool like this for windows is CDex http://sourceforge.net/projects/cdexos. Using this program you can rip the songs from the cd, and save them as an mp3.

Then taking the resulting mp3, you should be able to copy it to the 770 and the native player should play it. It's been a while since I've used cdex but there are (or should be) docs out there that you can read to get a quick feel for the program and how to use it.