How do I do this safely?

OK I have a static website and I want to know use wordpress to manage the site. The thing is the page structure for the current website is "http://domain/page.html". If I use Wordpress, it's going to looking something like, "http://domain.com/page/" without the .html ending.

Now is there a way to make wordress permalinks end with .html?
I know I can use a 301 redirect but will this pass on the links I have to the original site to the new wordpress one?

Yes, it's possible and very easy.

/%postname%.html

See http://codex.wordpress.org/Using_Permalinks and scroll all the way to the bottom where it reads "Having your posts end in .html"