I don't currently know PHP, but have used PHP based sites before (forums, WordPress, etc.).

I'm building a website for a company that is going to contain a variety of different collections: article archives, video and audio archives, as well as the more basic "about the company" pages.

Would PHP make this work better? Eventually there's going to be quite an expansive collection of work online through this site, and I want it to be easy to search, and consistent throughout.

If you know the basics (Echo, includes if's) you should be completely fine at creating a simple website. If you have no experience with PHP, but you have used html/css/javascript before php should be a walk in a slightly hilly park (A bit of extra work, but once you get to the top it's all down hill).

Wordpress itself with a bunch of plugins will be quite fine for creating a site with video and audio archives.

I would created a design code it using XHTML / CSS so it will easily integrate into WordPress. Mtishetsky brings up a great point - WordPress does have a wide collection of plugins you can use. By intergrating your custom design into WordPress it would save you alot of time down the road.

Creating with PHP is creating from scratch and it's very time consuming.
Try Joomla CMS.
It has components that do all those you need and more.
It allows my clients to manage website content by themselves and they love it because it is simple to use.