Prices are cheap enough right now that you might as well buy a new board. Check places like REI.com and sierrasnowboard.com for some sweet deals.
The best thing to do is demo a bunch of different sizes and styles so you have an idea of what you prefer before you buy. For example, after riding several different boards at various lengths, I know that I prefer and ride best on a shorter, flexier board.
For a beginner, the trick is to buy a board that you will be able to learn on, but that will be advanced enough for you to ride for a few years. I tend to recommend mid-range all-mountain freestyle boards for beginners - soft flex to learn on, but not too soft to hold you back as you progress.
Some plain or less girly boards that might suit you:
Never Summer Pandora
Atomic Fallen Angel
Arbor Eden or Cadence