1. You can use your Shimano 105 shifters with an Ultegra crankset & Ultegra front derailluer. The trick is to get the cable tension and limit srews set up correctly on the front derailleur, as you have a triple shifter and will be using it on a double crank. It can be done, but it may take some adjustments to get it just right.

2. I went from triple to compact double (50/34) on my road bike this year. I found the triple front derailleur to require too much fiddling with the double crank, so I picked up a compact-specific FD. I don't know if your results would vary b/c you are using a full-size crank, but in any case a good new Shimano double FD can be picked up for relatively cheap on eBay.

3. I know you didn't ask, but if you are (a) newer to biking (b) older than about 30, (c) have bad knees or (d) someone who rides in hills on occasion, talk to your coach and see what he/she thinks about a compact front crank (50/36 or 50/34) instead of a full size 53/39.

Thanks for both your info. I went to my LBS today and they will sell me a Shimano Ultegra double crank, Ultegra rear derailer (said my triple would not work) and front 105 double installed for about $255 with trading in my same components currently on my bike.

He told me I needed some bigger gears particularily a larger ring than a 50.

The rear does have a little to do with it, although changing from a triple to a double won't cause a problem....only going from double to triple will cause issues. Triple rear derailleurs have a long cage, whereas double rear derailleurs have a short cage since they don't need to pull up as much slack in the chain from there being a granny gear. A short cage rear derailleur used with a triple front will cause an awkward chainline, making it more likely that you'll drop your chain and speeding up the wear it gets. The only problem with having a long cage derailleur on a triple setup is a very minor weight penalty.