Jordi,
This is an old article I wrote and I would certainly update much of the info in it, however, the basics hold true for any underwater videographer and I hope you will find it helpful.
http://www.kenstone.net/fcp_homepage/underwater_douglas.html
Since you are on a Mac you will have 3 basic choices of editing software (NLEs), iMovie, Final Cut Express and Final Cut Studio. Final Cut Studio, now in its 3rd studio generation and 7th generation of Final Cut Pro is the choice of champions (and some not so champion) You can learn an awful lot by checking out the Final Cut websites like www.kenstone.net and www.lafcpug.org You will find many tutorials, articles and reviews there. The discussion forum on the kenstone site is the absolutely most responsive and anytime you have a question or problem regarding editing, this is the place to get answers quickly.
For training DVDs, the market which had at one time been barren, is now over saturated. In my mind, the best of the bunch are the training DVDs from Ripple Training.
For books, the Peachpit Press publishes both the Apple Training Series of books regarding all of Apple's applications and are also used as the basis for the Apple certification exam should you ever want that. Peachpit also published the Quicktime Guide for FCP by Lisa Brenneis which is the go to reference book for FCP.
There are many other books and dvds out there and most are very good but the ones I mentioned, in my opinion, are the best ones available.
Again, hope this helps.
Steve
40' vis on the Ruby E in San Diego this morning. That's great vis for San Diego waters. Of course, after 30 min. the vis dropped to about 15'