Anyone here know how to use a microphone when playing online with a buddy? What about if one buddy has Windows and one Linux?

teamspeak would be your best bet

which is at: http://www.teamspeak.org

Thanks Tyme but I find that very confusing on how to use. I don't understand it. Any other ideas or can you tell me how to use it. A simpler one might be more useful to me.

i haven't used it, so i can't really give you any directions, but you might find something helpful in the FAQ section they have.