Its supposed to be easy, right?

[eluser]gtech[/eluser]
I think you will find the default controller always works, this isn't a newbie question at all as it appears lots of people have had problems with this.

I think the URLS codeigniter uses are not compatable with IIS without using the ISAPI Rewrite.

what you could do as a test is enable_query_strings in the config/config.php and then browse to

www.your-site.com/index.php?c=controller&m=function

see if that works... the config file has a comment to show you how to use enable_query_strings

if that works you know its a URL style problem.