For video software it's really either free, or super expensive. There isn't much room for the inbetween. If you're just starting off making videos I recommend going with free software.
For windows I would recommend either Windows Movie Maker or LightWorks.
The former is a free tool by microsoft. Although it doesn't have all the features that a professional program will have, it does well at what it does and is super easy to use and get started with.
The latter is the free version of a professional grade application that was used to make movies like 28 days later and Hitchhiker's Guide to the Galaxy. It's rather limited compared to it's paid version, but has a lot of useful tools for advanced editors. The big drawback being that it can only output to a max of 720p.
For mac users I recommend just using iMovie. It's simple and has almost no learning curve, but still has some powerful tools built in (if you can find them).
As for audio editing, I can't recommend anything other than audacity. I use it myself and so do a lot of professionals, it's completely free and supports a wide variety of plugins.
The Meaning of Life, the Universe, and Everything.
Actually, a really good 'in-between' for video editing is Sony Movie Studio - it's a little more expensive than FRAPs, and will do everything you need it to for standard LPs (Vegas is its big brother, and for youtube content creation, there's almost no need for Vegas or other 'super expensive' editors)
And audacity is hands down your best bet for audio editing... there are other similar options (Sony Soundforge comes bundled with Movie Studio Platinum... and is about on par with Audacity... there are of course other audio editors out there...) - neither of these would really work for composing music, they're just for editing recorded audio tracks (if you're looking to compose music, you're wanting to look more at something like FL Studio, which is paid)
Best of luck.
PS - I would recommend sticking with the 'free' or 'cheap' options for at least 2-3 months, while you get a sense as to whether you enjoy youtube. And if you find yourself enjoying content creation, then invest a few hundred dollars into equipment and software upgrades (better mic, basic editor [like movie studio], extra HDD, etc.)