Taking random windows files off of the internet is not going to fix your problem. In fact it is only going to make it worse.
The best thing to try is to uninstall the game, then re-install and then patch to the latest edition. This shoufl give you a clean install and so error messages that are coming from the game and not from the random fiels you have downloaded.
Once you get the game reinstalled check out the Raven Shield website/ forum to see if anyone has the same problems as you ahve have already found out how to fix it.
during the installation process of Rainbow Six 3 this message is showed "Unable to find Raven Shield".
Is this a copied disc or the original. If it is a copy then use the original. If it is the original then the CD is dirst or scratched. Have you installed it before OK?. If you ahve just bought it then I would excahnge it for another copy and try that.