A few questions on rollers

After describing your abilities, I'd suggest that rollers would not be what you bargained for - I think they're difficult to ride on even for an accomplished rider.

I'd suggest a stable trainer over rollers, which will be much more confidence-building.

If you want recommendations, fluid trainers get high props around here and two of the more popular models are the CycleOps Fluid2 and Kurt Kinetic road machine (my preference).

Simply spending time in the saddle will improve your balance.  If you don't feel comfortable going down hills on the aerobars then don't.  Over time your confidence will build and you'll eventually be able to do it without any trouble at all.

I used to train on rollers many years ago when I used to do road racing, and I used to do roller races with other cyclists in the off season.

You can learn rollers, and yes your balance will improve dramatically: just start by leaning on a wall next to you, pedal up to speed, and gradually get your weight off the wall.  That said, I would not even think of trying aero on conventional rollers.   

I'm thinking of getting some e-Motion rollers from Inside Ride, which DO let you ride aero (see the videos on their website)

http://www.insideride.com/index.php?option=com_content&task=view&id=15&Itemid=36

Aero bars + rollers is a receipe for a fast trip across the living room-and then crash into the plasma TV.

I love rollers, but not for a tri-bike.

Get some rollers!  It will only set you back about $100 if you get them from Performance or Nashbar, and they will do wonders for your balance.  I've had some for about 2 years, and I went from having a death grip on the bars to being a lot more comfortable.  I've really gotten better riding one handed, taking drinks, and looking to my sides and behind me.  Rollers teach you to be relaxed on the bars and smooth on the pedals.  It can be frustrating in the beginning, so set them up in a doorway so your shoulders bump into the door molding if you go too far to one side. 

Don't let people scare you about rocketing off into your living room.  That won't happen even if you did go off the front of the rollers.  Your wheels would just stop.  You may fall over to the side, but that's just extra practice for unclipping quickly. 

To the OP, rollers are probably not for you. It is more difficult to ride rollers than on the road as you don't have momentum to help keep you upright. However, if you get and conquer rollers, riding on the road will be no problem

They're really not that bad. I chose rollers over a trainer my first winter of triathlons (3 yrs ago and was a complete bike newb). The best advise I can offer is ride relaxed and don't think about falling. If you are tense or think you're going to ride off, you probably will. Riding aero isn't very difficult, but there is a leap of faith you need to go from bullhorns to aero.

I've fallen a few times, but it's mostly when watching sports.

For roller inspiration, check out Wii Sports on rollers .

Personally I feel like rollers have done wonders for my ability to ride a straight line, have balance, AND be more comfortable in aero bars.  It definitely took a few falls before I was comfortable in aerobars on the rollers, but now I do it regularly.  Sure I still crash on them every now and then, but I keep doing it and keep getting better.  My thought is that if you are going to do something in a group ride (be it just ride straight, ride in aero, take a drink of water, whatever) you should be able to do it on rollers.

good luck.

p.s. for those wondering I have hand-me-down nothing special at all rollers.