.htaccess or .htpasswd equivalent on IIS?
Solution 1:
For .htaccess rewrite: http://learn.iis.net/page.aspx/557/translate-htaccess-content-to-iis-webconfig/
Or try aping .htaccess: http://www.helicontech.com/ape/
Solution 2:
There isn't a direct 1:1 equivalent.
You can password protect a folder or file using file system permissions. If you are using ASP.Net you can also use some of its built in functions to protect various urls.
If you are trying to port .htaccess files used for url rewriting, check out ISAPI Rewrite: http://www.isapirewrite.com/
Solution 3:
I've never used it but Trilead, a free ISAPI filter which enables .htaccess based control, looks like what you want.