I need to create rules for web.config that will rewrite all requests for files with extension .html to .asp and redirect all .asp requests to .html

Example:
file_xyz.asp rewrites to file_xyz.html
directory1/file_xyz.asp rewrites to directory1/file_xyz.html
and

file_xyz.html redirects to file_xyz.asp
directory1/file_xyz.html redirects to directory1/file_xyz.asp

1. What is the syntax for the rule
2. Is this too broad a rule? If I should need for what ever reason to have a physical file such as file_abc.html how do I exclude it from the redirect rule?
3. I am thinking I should just use ISAPI_Rewrite http://www.isapirewrite.com/ there seems to be a ton of resources out there for rewriting with htaccess and very little online help for using IIS 7 URL rewrite. Any thoughts and/or advice

Thanks in advance