Further to my post called Webpublisher on Windows Vista, here is how to install Inmagic Webpublisher on IIS 7 in a 64-bit environment such as Windows Vista x64 or Windows Server 2008 x64.
These instructions are valid for DB/Text Webpublisher as well as CS/Webpublisher. Steps 1 - 5 are valid for 32-bit IIS 7 as well.
1. Ensure IIS is enabled
This screenshot shows which IIS features are enabled on my Vista x64 machine. The highlighted one is particularly important (IIS metabase and IIS 6 configuration compatibility).

2. Install Inmagic Webpublisher
Follow the usual Inmagic install instructions.
3. Enable ISAPI-dll handler mapping on dbtw-wpd or ics-wpd virtual directory
Open the IIS Manager.
Open the Handler Mappings for the dbtw-wpd or ics-wpd virtual directory. (Figure below shows dbtw-wpd.)

The ISAPI-dll handler is disabled by default.

Enable the ISAPI-dll handler: right-click it, choose "Edit Feature Permissions", and check the "Execute" box. Click OK.

4. Set the Webpublisher dll as an allowed restriction
In the IIS Manager, click on the machine root - this is the top level of the tree in the left column, which shows the machine name. You should see a number of machine-level features, including "ISAPI and CGI Restrictions", as below. If you do not see "ISAPI and CGI Restrictions", you have not properly enabled IIS settings in step 1.

Open ISAPI and CGI Restrictions.
You may see Inmagic Webpublisher as an allowed restriction already. The path will point to the install location of dbtwpub.dll or icswppro.dll, depending on which version of Webpublisher you installed.
If you do not see Inmagic Webpublisher as an allowed restriction, you must add it. (Figure below shows DB/Text Webpublisher.)

5. Create an application pool for Webpublisher
Open Application Pools from the IIS Manager.
Add a new application pool to be used with Webpublisher, called "WebpublisherAppPool".

Go to the dbtw-wpd or ics-wpd virtual directory and open its Advanced Settings. Set the Application Pool to the new WebpublisherAppPool just created.
6. Enable 32-bit applications on the Webpublisher application pool
Open Application Pools from the IIS Manager.
Right-click on WebpublisherAppPool and select Advanced Settings.
Set "Enable 32-Bit Applications" to true. Click OK.

7. Get a drink. You're done.
Whatever drink you like. I like red wine, or on a hot day, gin and tonic.
Some more explanation
Whereas in IIS 6 you could run worker processes in either 32-bit or 64-bit mode, but not both, IIS 7 can run 32-bit and 64-bit worker processes simultaneously. And, as the above instructions make implicitly clear, you can set this behaviour on individual application pools.