THE PROBLEM:
I ran into an issue a few weeks back that had me puzzled. I was attempting to publish some InfoPath forms to a demo MOSS site as browser based content type InfoPath Forms. When I fired up the publishing wizard the option to publish them as browser enabled forms to SharePoint was disabled. I could not figure out what was wrong and it took me a while to realize the cause.
THE CAUSE:
It turns out I had deleted a necessary form library on the SharePoint server in my desire to "clean" up my demo server. Without that library's existence the InfoPath client will not allow the publishing options to be enabled.
THE SOLUTION:
So the lesson here is that InfoPath Forms Server requires a form library called "Form Templates" on the top/root site of the destination SharePoint Site Collection in order to support publishing. Fortunately I was able to recover mine from the Recycle Bin.
Hope this helps someone else...