I'm wondering if the "new and improved" file creator standard for Snow Leopard has messed you up here, though I'm thinking your installation of XAMPP may have helped a little.
Under Apple's System Software and their OS X operating systems up to Snow Leopard, file creator and "application to open with" information was stored in a file's "resource fork." In order to be more Unix-ey or, perhaps, just to mess us all up, Apple has done away with the OS hooks to the resource fork and is merely using the file extension.
Try using "Get Info" to redefine the file (on the OS level) as something to be opened by Dreamweaver.
Another workaround is to open the file in a text editor by dragging and dropping it into TextEdit, then opening Dreamweaver, creating a new file (CSS) and then doing a cut and paste of the code from the text file into Dreamweaver. Do a Save As and then reattach the style sheet.
That's a PITA, but it should get you there.
I attempted both of these strategies, but to no avail. When I click "Save As", the icon is correct in the finder. However, in the Files Panel, the icon is different. I get the 'stacked boxes' icon in the Finder, but I get the <-> icon in the Files Panel.
Is it opening correctly in Dreamweaver? Is the style sheet correctly connecting to the HTML (or Server-Side Code) pages you are making?
If OS X doesn't place the right icon on them, I don't really care. I have XML files that, since I installed final Cut Studio come up with an icon that one would associate with Final Cut Pro -- and, indeed, XML is used in Final Cut Pro as its edit decision list.
What is important is that the file have the correct association with the application you mean to have open it. The rest is simply window dressing.
The pages are not attaching appropriately. Also, whenever I update the style sheet or page template, the change does not regoster on the other pages. I lose formatting (styles) on pages associated with the template or the .css file.
I really appreciate your help!
I suppose this serves as a warning to not install XAMPP.
Here's what I would do if things are just not connecting...
Dreamweaver keeps a record of everything in a cache file for that website. I think your cache might be messed up for that site.
Make sure that all links to your css files and templates are good.
Then in the menu under Site>Advanced, have Dreamweaver recreate the site cache.
That may cause everything to link up again properly.
The only other suggestion I have for you is to recreate the site from scratch and that is a lot of work.