I'm using Code Igniter and rewrite is an option and you are not forced to use it. When not using rewrite, the url's will be something like this(with IIS):
http://www.yoursite.com/index.php?/controller/
Having said that, I have never had to run pages on IIS server but from the CI forums I found that you have to add that extra ? after index.php in the config. With other webservers you dont need that.
I can warmly recommend you to try CI. Its so easy to setup that it wont take you more than 10 mins, thanks to its high quality manual 😉