UMMMM . . . . I'm not sure if you can get the free download of 06 without having 08 already installed on your computer?? Since you can't install iLife 08 on your G4, this could be a problem that maybe someone else may know the answer to.
IF you could find a copy of iLife 06, maybe lying on a storeroom shelf at an Apple dealer, or on eBay, that would be the next best solution. Failing that, or a solution to the first problem above, you may be using iMovie HD (05) a while longer. Not that there's anything wrong with that, for you could go to the Gee Three website and find a whole lot of plug-ins, for a fee, that provide extra transitions, titles, video and audio effects that will work with your iMovie.
Good choice on the camera too, although I have seen threads here that talk of issues with getting the most out of a high def camcorder vis a vis the computer handling the files and also the availability and cost of HD DVD burners. Just a heads up on that one.
Forest