This is NOT a slam on any writer. I do, however, suggest you read this and keep it in mind when you write a story.
As MJN mentioned in her Story Guidelines Post, please, if you're unsure of the grammar or punctuation for a story, find a beta (basically an editor). Betas don't change what you write in a story, in so much as they don't tell you WHAT to write, but give you some ideas on HOW to present it so that others will want to read it.
First off, before you post it here (or fic in any message board/website), write it out in a word processing program, such as MS Word, Corel WordPerfect, OpenOffice Writer, (or equivalent on a Mac). This way you can easily do a spell and grammar check. Though those are not fool-proof. You can cut and paste the story into the message board when you're finished. It aslo allows you to go back and forth and change things if you need to much easier.
I will offer to beta, and I'm sure that there are others on the MB who would as well, because we certainly do not want to stifle the imagination of the writers. I have written stories in other fandoms, but not yet in BG fandom, primarily for the fact that others seem to do a much better job of it than I (ex. MJNet, ILMJN/Larkhall Returns, CanadaBadGirl, Gina L. Dartt).
There are some fantastic suggestions out there to help with the grammar/punctuation as well, when you're starting out writing - and even as a fun check when you're an experienced writer.
English Chick's Guide to Grammar - this site uses a lot of Xena references, when referring to grammatical errors and suggestions. It's how I got to know her via a XWP e-mail list as well as another list. She's got some really good points in there to help with grammar.
Holy Mother Grammatica's Guide to Good Writing - this is another brilliant fan writer's guide to good writing, using a lot of fan references. I went a panel for HMG at MediaWest a few years ago and it was absolutely brilliant. 2 hrs long and we had a ball.
Lori L. Lake's Writing Links - Found this a good site for all kinds of writing help and suggestions.
Now, go forth and read, then write!