Bike Options

I just decided to do the Chicago triathlon next year, so I'm starting to prep training schedules / gear. I currently have a TREK 2600 mountain bike - nothing fancy, it was like 300 bucks at the bike shop a couple years ago. It has served me well, and I was planning to ride it (with perhaps minimal mods - seat, handle bars, wheels) in the event. I recently came across the opportunity to obtain a 2008 Specialized Crossroads Sport hybrid bike - also not fancy or expensive, it retails for about 400 bucks, but it's a hybrid instead of mountain bike.

My question is this - is anyone familiar with this Specialized bike? Would anyone recommend it over a TREK mountain bike for use in the tri? Are hybrids typically lighter than mountain bikes? Would a better option be to just swap out the wheels on my TREK? I'm basically in a position where I can get the new bike in exchange for something I was selling anyways, but I don't necessarily want a second bike if it's no better for my purposes than the one I already have.

Thanks!

David