Video Editing Software Help?

I have an idea for a video that I'm going to make for my girlfriend. I'm a musician, but I've never used any kind of video editor other than WMM. For what I'm trying to accomplish, I'm going to have a ton of voice clips and sounds to put all together into one video, plus some video playing throughout. I'm not sure what kind of software I need for this. Do I need a video editing software or some kind of audio editor? And what are the best programs for this type of thing? Preferably something I can download for free, but I'll pay for it if I have to. I'm really serious about doing this for her, so any info is appreciated. Thanks.