It's kind of an all or nothing situation. Either you get the mixed bag of helpfulness that is the Rich Text Editor, or you're on your own with the BB Code Editor. You can entirely turn the RTE off in your Preferences menu by deselecting the "Use the rich text editor to create and edit messages" option. EDIT: Ninja Greenie beat me with this info with a helpful image guide. :o
However, you can bounce between them to get the best of both worlds. I usually have a copy of my posts sitting in a Notepad just in case something is broken when I go to preview it in the Rich Text Editor, which then leads to me swapping to the BB Code Editor to see what's wrong so I can go fix it in the Notepad version that has not become garbled by the RTE. That minimizes the problems I encounter with the RTE, because I never have to deal with all the extra coding chunks it likes to add in when something is broken.