I just purchased Sony Vegas 7 after using Windows Movie Maker for some time. It previews fine just playing a clip, but when I add transitions and film effects the preview stuttering becomes so bad I cannot productively use the program. I suspect my PC is not powerful enough. My specs are Celeron CPU 2.4 ghz, 1 GB of ram. I have 20 gigs of free space available on my hard drive. Time for a PC upgrade maybe? If so, what minimum specs would you recommend?