YACMS + Multiple Templates

I'm in the process of building yet another content management system with PHP/mySQL/XHTML/CSS. I'd like to have the CMS input fields change based on the template. Any ideas?

Basically, the CMS should be generic. It should look to see what the different templates are that are assigned to the current site and display input fields based on which template is selected. There could be multiple templates (home, news, contact, etc.) for each site so I can provide specific templates for different clients. This also gets into setting up the database properly, so I imagine it will be fairly complicated. Maybe a different database for each template or template set?

One thing's for sure, I don't want my clients to modify the templates from within the CMS, like you can with MoveableType.

I'm having difficulty describing this, so ask questions if I'm not clear. Also, I'm looking for inspiration/direction, and not necessarily specific answers! Thanks!