You can use RewriteCond to determine if the requested is a directory or a file. What would probably work is a:
Code:
RewriteCond %{REQUEST_FILENAME} !-f
And proceed with your matching rules. That should only apply the rewrite rules so long as the requested file is not an actual file.
For domains, you can also use the RewriteCond to match hosts. This would allow a one line swap when you change a domain.
I hope that helps some, I'm not an apache wizard but I can typically stumble my way through.