That's why I said emulator. I should have searched before posting, but apparently there is already at least one product on the market that does this (Helicon Ape).
I think what I did, when I was using lighttpd with Wordpress, was to look at the .htaccess files that were being used, then translate them (by hand) to lighttpd rules. It requires a bit of expertise in both Apache and in whatever web server you're using, but it's another solution to consider if you're looking to "use" .htaccess files.
Are you looking strictly for mod_rewrite syntax support in IIS?