<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
                <rule name="Index">
                    <match url="^(.*)$" />
                    <conditions>
                        <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
						<add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" />
                    </conditions>
                    <action type="Rewrite" url="index.php/{R:1}" />
                </rule>
            </rules>
        </rewrite>
    </system.webServer>
</configuration>

This will allow pretty url for codeigniter running under IIS7

Codeigniter IIS7 Web.config

Other