hmmm, i dont know alot about this, but i use windows movie maker if i just wanna edit a bunch of clips fast, cuz i think WMM is the easiest editor out there, but theres no cool effects, so if your going for a artistic video, then i would sujest Sony vegas 8, it will take you 30 minutes to make a video that using WMM would have taken 15, but i think that if you want a Great video editing then vegas is the way to go.
PS: i dont edit any of my videos though (a friend of mine does) XD