Yes, definately play around with iMovie, you will soon want to move onto more powerful suites.
I started out on iMovie, then went onto Adobe Premiere, now i'm a Final Cut Pro user, definately the best progression.
If you start with iMovie, which comes free with every new mac, you could then look into Final Cut Express, a watered down version of Final Cut Pro.
Studio may be overkill if you aren't familiar with it already. It is a complete studio package, audio mixing, motion graphics, pro DVD authoring...
Rich.