external redirect plugin

Is there a plugin which will add something like redirect.php?url= to all external links in a post? I’m looking for something to do this where it would just ereg_replace() or something the URLs so it would show that redirect.php…it would need DDoS protection and only allow redirect.php to work from the source domaint that the blog was being hosted at…but still, I’m looking for something of this manner….anyone know of a plugin like this?