Protools is a blessing and curse. The curse is expensive. The blessing is it works beautifully and is much easier to learn (in my opinion) than the PC counterparts. I strongly recommend if you do Protools you do it on a Macintosh. Others have had good success with the "light" Protools hardware which will run you $700-$2500 range not including computer. I recommend you spend the $15K or so and get a Protools HD|2 setup. For that money you can afford a decent Mac and monitor, a hardware interface (96 I/O maybe - 8 adat I/O, 8 analog TRS I/O) - you can also get some kick ass plugins. Protools TDM plugin architecture means you're reverb etc. instances are handled on the Protools hardware not on your Mac's CPU which means real time effects with near zero latency when monitoring - a huge plus.

You'll also be compatible with the pro's out there. A lot of people in this group will shun Protools because of the price but no one denies it is the industry standard. Get Protools: be happy: make more money with your clients.

I recommend the following online video which demonstrates loop editing in Protools and will give you an idea.

http://www.mtsu.edu/~nadam/downloads/PTlab3web.html

Requires Quicktime which you can get free from http://www.apple.com

Cheers!