Do be aware regardless of this that every graphics tablet manufactutrer pretty much uses their own proprietary protocol.
There is one old standard (MM-1201)., but it's not really used much anymore, so you'll want to make sure that whatever drivers you can get ahold of specifically say which tablet models they support.
WACOM (pronounced Wah-kum, not WAY-KOM) tablets are generally considered the best by most users.
