Tri Bike vs. Road Bike (expert advice needed)

The topic of road bike vs tri bike has been approached MANY times on BT -

http://www.beginnertriathlete.com/discussion/search/query.asp?fid=0&action=search&searchforumid=1&keywords=tri+bike+vs+road&mode=1&subjects=1&messages=1&author=&days=1&datemode=3&custom-start=&custom-end=

The way the question was asked, it almost sounds like a troll.  This is such an open-ended question with nothing provided from you as what capabilities, times, level, doing more races strictly that have flat roads over races that has tons of hills, etc. etc. etc.

A Google search brings up the following:
http://www.google.com/search?hl=en&q=road+bike+vs+tri+bike&aq=0&oq=road+bike+vs+tri&aqi=g1

So, how can anyone possibly give you any insight?

BTW, I apologize for my analness, but the word is TRIATHLETE, with no "A" in the middle.

All the arguments for this debate seem to primarily consider the type of riding you do outside of races versus what raced you do.  Understand the differences, pros and cons of each then consider the type of riding you will do.  Finally decide for yourself.

OP, road bike with areo bars.

You can do fine in any race, at any distance, with either bike as long as it fits properly. 

Tri-bikes are often a little more expensive for the same level components. 
Tri-bikes are often a little heavier because they sacrifice weight for aerodynamics. 
Integrated brake/shifter levers (road bikes) are considerably more expensive to replace than the bar end shifters/aero brake levers. 

Tri-bikes are not allowed in most bicycle races and are unwelcome in some group rides. 
Steering dynamics can be different and tri-bikes may not be as well-behaved in an evasive maneuver because of the rider position and front/rear weight distribution (this, the brakes not being under your hands, and the potential to get skewered by the forward pointing bars are the reasons tri-bikes are discouraged in group rides). 

As a beginner, you may be hard-pressed to point to the difference in bikes as the reason you gained/lost positions in the race (as opposed to general fitness or race strategy). 

It is a matter of preference and taste.  For the pros, it is essential to shave off time and to save energy in the process.  So a tri bike is a must for the longer triathlons.  For us mere mortals, it does not matter that much.  After all, what's a few seconds more or less?  A tri bike does not offer much advantage in a sprint.  Actually you would probably be better off with a road bike there.  Coming from a cycling background, I only actually put aero bars on my road bike for olympic triathlons.  But, by my third season, I wanted to do a half-iromman.  For this, I started the season with a Cervelo P2SL, which saved my legs for the half-marathon after the 90km bike ride.  (I have a road bike, a tri bike, a mtb and a tandem ... one for each occasion.)

On the technical side, here is the difference between a tri bike and a road bike:

http://www.bikesportmichigan.com/bikes/difference.shtml

In no way am I an expert, but I just went from a 15 year old mtn bike to a nice used Quintana Roo tri bike.  I was in the same position as you, but mine came down to what I am planning on doing with the bike.  I don't think I will do group rides as most of my "training" is either by myself outside or on the trainer in the basement.  Also if tri bikes are supposed to help save my legs for the run, I need all the help I can get.  Plus tri bikes just look cool and are a lot faster than a hand me down mtn. bike.