Moodle has a wonderful "algebra filter" which can easily make mathematical expressions in classic layout. I'm surprised that no one has written it up here! The filter is included in the standard Moodle packages. The administrator must activate it though before you can use it.
I personally think that students should be taught to recognize and use expressions that can be written in one line just the same as one enters them in a spreadsheet or when entering on a calculator. Having that ability also increases the ease of making interactive math problems.
The algebra filter can take expressions written in that way (like you would enter them i a spreadsheet cell) and display them the way we usually write them by hand or in math books. You simply surround the expression with double @:
Unfortunately this Moodle Docs Site doesn't have the algebra filter (activated?) so you can't see here how nice they look. (There is a LaTeX math formula button in the wiki editor, but it doesn't recognize TeX or Algebra filter expressions, and I don't find any docs for THAT either!)
For more advanced expressions that the algebra filter doesn't cope with there is the TeX filter that can basically do any math expression. The syntax there is more complicated. and the expressions are surrounded (in Moodle) by double $. Here is a good wiki about TeX notation: http://meta.wikimedia.org/wiki/Help:Formula
(The algebra filter is actually a simplified front end for a TeX engine)