Have not tested it yet, but the looks are better than the one Alex mentions.
The description at winginx.com/en/htaccess says:
About the htaccess to nginx converter
The service is to convert an Apache's .htaccess to nginx configuration instructions.
First of all, the service was thought as a mod_rewrite to nginx converter. However, it allows you to convert some other instructions that have reason to be ported from Apache to nginx.
Note server instructions (e.g. php_value, etc.) are ignored.
The converter does not check syntax, including regular expressions and logic errors.
Please, check the result manually before use.