What programs (preferably freeware) can synchronize a video recording with a seperate audio recording?

I'd like to make a youtube video of me playing a piano piece (yeah, I know, I have too much free time), but I have a microphone that is much better than the one on my webcam. I can disable the webcam's microphone, but is there a way for me to synchronize the sound and the video files? I tried windows movie maker, but I can't seem to synch it there (my fingers and the notes always eventually go out of synch) I guess I'd have to do it manually in the worst case... Thanks in advance!