You might want to PM RammSPOOn. SPOOn does it a lot with DeviantART, so that'd probably be the person to ask.

Depends on the medium. The thing about Traditional art (the stuff not done on the computer) is that you need to scan it to print it. The problem with scanning is that the light that is used adds a bluish tint to the works, and I can't begin to tell you how many complaints I hear from people when they scan their colored stuff.

It is, however, easily circumvented with the aid of a decent art program that'll adjust color tones.

That said, once it's scanned in it's a matter of resolution and DPI settings to get it to print to something bigger than a 8.5 x 11" piece of paper.
300 DPI is recommended for anything slightly bigger than 8.5x11", but if you want poster-size you should consider 600 DPI or even higher. DPI determines quality of the image when it's scaled up like that. A 150 DPI image will look like crap on a 15x30" piece of paper, whereas a 600 DPI scan will look much crisper.

So once you determine what resolution you need, take the file to Kinko's or something and have them print it out. :D Won't be cheap, I promise you.

That's the basics of it, anyhow.

XXX and DPs are in order.

Ok...I know about the XXX thingies...DP? Um, ok sure, if it's a good thing, why not

Thanks SPOOn, really appreciate it. The friend I am talking about mainly does oil paintings and chalk, and he sells a lot of his work. He heard about selling prints, and wondered how viable that was, as well as how to go about doing it. I wasn't sure what to tell him, and I was kinda curious about it myself.
Thanks for the great advice and solid foundation. I'll check it out for sure.