Atomatic link generator from page content

I require a script that will scan the content of a page and automatically convert certain keywords and phrases into links. For example, each time the word "contact us" appears in the text, I would like it to automatically be converted into a link to a page named contact.html. Ideally, I would like all these automatic links to be listed and controlled by a single javascript file, and simply by updating this one file I could control the links throughout the site (so long as each page calls the original javascript file) The site itself is really quite basic (plain old HTML). There is no database and no plans to include one. In total, I would estimate there would be somewhere in the region of 250 keyword/links although I would just require the coder to demonstrate the code works by making links to one or two keywords. I would then follow the principal to generate my own content and links.