Nothing screws with a message board database quite as much as users changing their names. Especially when they want their post count to stay the same, and want credit on the various posts and replies they've made, etc. I've only been running a message board for a few months now, and I dread when a member asks that, but I do make exceptions. I know that Dan does too, and I'm sure if you asked him, he'd try and help you out. A little friendly advice, though; think long and hard about what you want it to be, because no webmaster enjoys getting that request over and over again from the same guy.
