Did you mean convert an existing static html site to dnn?  If so,

1) You could pay to have it done.  From what I've seen, some services are relatively inexpensive.

2) You could buy a skin that has a similar layout to your static site.  Make sure you take into account how the navigation is set up in the skin you purchase.  You would want something that closely resembles how your static navigation is set up.  You would then be left with creating your pages and copying over your content.

3) You could modify one of the existing default dnn skins.

By static, I'm assumming the site doesn't have a lot of interactive usuabilty features.  If your plan is to take some existing static content and make it a more dynamic experience, I would plan on taking some time reading and testing various modules that fit the bill for what you're trying to accomplish.

If you meant move an existing static html site to dnn, in my mind this is the same as converting the site since dnn dynamically renders content through one default.aspx user control.

Hope this helps,

Paul