PHP Auto-Linking Site-Wide

We are not sure what is needed to do this but we need you to come up with a solution: We need our site to automatically turn specific words into hyperlinks, linking to our chosen urls. A good example of this function is in the phpBB word censor system, which lets the ADMIN chose a word like "forex" and have it replaced with something like forex Can you do this? Please only bid if you are confident and can do this fast Thank you!