Having worked with both Helicon rewrites and the native rewrite engine developed for IIS7 I must say the URL Rewrite Module is a lot more powerful and versatile, some software it does not seam to work with very well, like magento and even Wordpress to an extent was hard to get to work but worked with some necessary tweeks.
Modx has been the easiest software package to write a set of rules for to date and we are more than happy to share these with the community so people using IIS7 servers can use the SEO links and all the Modx features with no troubles.
<rewrite>
<rules>
<rule name="ModX IIS7 Rule 1 (By Simon Fraser)" stopProcessing="true">
<match url=".*" ignoreCase="false" />
<conditions logicalGrouping="MatchAll">
<add input="{HTTP_USER_AGENT}" pattern="^.*internal\ dummy\ connection.*$" />
</conditions>
<action type="CustomResponse" statusCode="403" statusReason="Forbidden" statusDescription="Forbidden" />
</rule>
<rule name="ModX IIS7 Rule 2 (By Simon Fraser)" stopProcessing="true">
<match url="^(manager|assets)" ignoreCase="false" />
<action type="None" />
</rule>
<rule name="ModX IIS7 Rule 3 (By Simon Fraser)" stopProcessing="true">
<match url="^(.*)$" ignoreCase="false" />
<conditions logicalGrouping="MatchAll">
<add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" pattern="" ignoreCase="false" />
<add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" pattern="" ignoreCase="false" />
</conditions>
<action type="Rewrite" url="index.php?q={R:1}" appendQueryString="true" />
</rule>
</rules>
</rewrite>
We have these rules currently running on two Modx IIS7 based websites and are having no problems at all and can see no difference from our Apache hosted Modx websites.
Hope this helps anybody having problems with IIS7 rewrites.
You only need to make sure your host has the URL Rewrite Module installed on their servers, most good hosts will have this already installed.
http://www.iis.net/expand/URLRewrite