Is there a limit to the length a post can be? It seems when I try to post more than a short paragraph I can't preview it and I get a screen that says "Internal Server Error" if I try to post it.

Shouldn't be a problem. I just tested with a pretty long (50 lines or so) post and worked fine. Sometimes if copy/pasting from somewhere else hidden code can cause problems...better to paste in notepad first then re-copy/paste from there.