How do you Define Extra Keys for X?

baadpuppy asks: "Ok, so I bought this nifty (and cheap) keyboard that has 'Internet multi-media' features: silly little buttons that do things like BACK in your browser, and scrolling, and controlling your CD and volume, etc. It was only 19.95 and had a $10.00 rebate, so I figured 'what the heck, it's only 10 bux wasted if I can't use them'. I read keyboard howto, and got the keys recognized by the Linux kernel, and everything is groovy for console apps. However, I spend 99.99999% of my time in X, not at the console, so I want to make these keys work in X. I have the list of scan codes (the kernel was kind enough to list them when it didn't recognize them). What has to be done to make X understand them? baadpuppy continues...
"I looked at the "XKB" extensions, and if there's any good documentation there, it's well hidden. I've downloaded the source code for the X server, and spent more than 5 hours perusing that code trying to figure out exactly where I might go about adding these keys!"