What license is the sound and graphics under? I'd like to use some of the graphics and sound effects in some of my own game development experiments as I'm neither artistically or musically inclined.

The complete game (including but not limited to audio and graphics) is licensed under the GPL v2 !

However for a game i learned its best NOT to use assets of other games because it will make the impression that its just copied. I have no idea how much stuff you might want to 'borrow' (which is technical ok as long as you honor the GPL) but if you except the find others to help on the game be aware that they might get such a wrong impression.
As i'm not a mapper myself i do not really know were to look but i know there are several online resources for textures and audio files.
Also please be aware that what ever files you find online have a certain license so make sure to know IF you can include them into your game without legal problems. BTW which license will your game have?

I'm not sure but it will be open source and free

Uhm.... do you mind telling us more about your project?

and if you don't want to talk this in public, please PM me.