You haven't neccessarily made a bad decision, but editing this with IMovie will require some extra steps. I'm not a mac user, but this link may help
http://forums.macrumors.com/showthread.php?t=195753
Those .VOB files etc is standard for a DVD-video. Some editing software supports editing a DVD-Video directly (e.g. you have a command like "open camcorder disc"). Others will edit it by simply renaming the .VOB files to .MPG... some if you do this you will be able to edit the video but may have issues with editing the ac3 audio...
My opinion - if you are generally going to edit on the PC, a DV cam would have been better... IMovie would capture that directly, it will edit more easily. The main advantage of DVD camcorders is the ability to shoot and have a disc without editing. Though you can also edit them... either change to software which supports this directly, or learn how to work around it wit IMovie.
Mark