Other quick links:
A. Thanks for asking, but it's really not up to me. All Forgotten Realms characters are the property of Wizards of the Coast, and only they can decide when a story about any given character will be written, and who will write it. If you're thinking of writing a story about one of the characters I've created and submitting it to WotC, stop now. Seriously. Don't do it. Editors want to know what sort of characters YOU would create. Also, there's an unspoken rule--actually, it's more of a guideline than a rule--at WotC that novelists generally don't write about characters another author created. (There are exceptions, of course. Most of the NPCs (non-player characters) in the setting were created by Ed Greenwood, so it's difficult to talk about existing characters without mentioning at least one that Ed created. Even so, writers keep away from his signature characters, particularly Mirt the Moneylender and Elminster. )
Let's assume that you just want to write the story--you have no intention of submitting it to WotC. That's fine, as long as you write it for your own enjoyment, and perhaps share it with a couple of like-minded friends. But if you post it on the web, you're publishing it electronically, and that may be a violation of copyright. A lot of people believe that if you don't make a profit from fanfic, it's perfectly legal. That's not necessarily true.
Admittedly, this isn't a clear-cut issue. There's a considerable amount of debate about the legality of fanfic. Some argue that it falls within the "fair use" description, others maintain that ANY unauthorized use of copyrighted characters or settings is a violation of copyright law. But one thing seems to be certain: for many publishers and writers, trying to protect their rights to their intellectual property would very likely cause more trouble that it's worth. This can create hard feelings among fans and negative buzz on the Internet.
There's a widespread misperception about First Amendment rights. Many people seem to believe that the First Amendment guarantees them the right to say or publish anything they like, anywhere and anytime. I would strongly suggest that these folk Google the Bill of Rights and read it for themselves.