This configuration is called Microsoft IIS – Domino SSO. Here is part of the help documentation. You will need to have IIS front-end your Domino site (Domino HTTP still runs, it just runs on a different port that you direct traffic to with the WebSphere plugin that is described in Help.)
We have been configured in this way for at least 5 years and it works quite well. We have 6.5.5 on our servers.
<b>Lotus Domino Administrator 6.5 Help</b>
<b><i>Setting up Domino to work with Microsoft IIS servers</i></b>
To use a Microsoft IIS server as a front-end machine, you must install the WebSphere Application Server 4.0.3 plug-in for IIS on the IIS server. The plug-in files are packaged with the Domino 6 server and must be copied from the Domino server to the IIS server. After you copy the plug-in files, you must configure the plug-in, then configure the Domino server to work with the plug-in IIS. You do not need to install any other WebSphere components to use the Microsoft IIS plug-in.
Good luck! Call Notes support if you run into problems. They are very helpful.