I'm thinking of buying VideoStudio 9, but I need to know if I can import my own audio source into it, and then add that audio to the video I'm working on.
What I want to do is take a silent movie and add a musical soundtrack to it.
Yes you certainly can. VS9 allows you to import audio from CD's or files on your computer in several formats, such as WAV & MP3. However there have some posts on how using MP3's can cause VS9 to throw tantrums.
...and not to forget that you can do the opposite: start with digital, colour video, and apply the 'old film' filter to get it monochrome and flickering, just like an old silent movie! I have used it to great effect a couple of times, seguing from what looks like a period piece into modern (coloured) times!