Have you tried Google?

Perhaps this will help:
Static Site to WordPress: The Definitive Guide to Moving Your Site!

PS: This tells how to 301 redirect your old pages

I would try and keep the old pages. You might be able to have wordpress and keep the old pages in tact. The current pages probably have backlinks and you will lose the value of those links if those pages disappear. It will be difficult to maintain the same page structure in Wordpress that you have with a HTML site.

Setting up the re-directs is the most important part, because the WordPress Permalink structure creates different URLs from what your current site uses.

Here's another article that goes through the entire process step-by-step:

HTML to WordPress: How to Convert Your Site

Cheers,

Martin.

If your site already ranks good and you're looking to move a static website into Wordpress, the biggest thing you'll need to worry about is site speed. Static websites don't need to access a database but wordpress websites do.

When a site needs to access a database or an external source, chances are, it'll load slower. This is otherwise known as making calls to the database. If you already know the answer and don't need to call anyone, your response is faster, right? Same goes for websites.

Site load times can really affect your rank depending on the niche you're in.

However, there are ways to make database sites load fast. The most well known, would be caching. If you're going to use a wordpress website where you receive tons of visitors or would like it to load faster in general, use caching. Not only does this help with speed, it helps reduce the load of bandwidth used.

I recommend one of the following two:

WordPress › W3 Total Cache « WordPress Plugins
WordPress › WP Super Cache « WordPress Plugins

Google and other web search engines actually favor websites that cache their content. Google wants to provide its users with the fastest most relevant content.

Another thing that can help is a reliable web hosting provider.

I've tried Go ..Daddy, Host Monster, Just host, InMotionHosting, Amazon EC2, Rackspace, and more.

For everyday people, I would recommend InMotionHosting. I've found that their servers stay fast no matter how long you're with them. Others may agree or disagree but that's just my opinion. Who you host with can really affect your business.

If you're an experience web professional, I would recommend looking into Amazon EC2 or Rackspace once you being to really get things going.

You may also want to look into Content Delivery networks (CDN).

I don't want to overwhelm you so for now, I recommend just sticking with caching your wordpress site. Its invaluable!

I hope this helps