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Don't know of any module that can do this. To do this ALL conecnt would have to be parsed through some sort of filter to search for your specified words, and then match them to a link. This will have a performance impact on your site. If you're using IIS you can probably do this without to much fuss using an ISAPI filter as it would also minimise the performance cost, and have no doubt that you can do something similar with Apache.