URL Rewrite with MicrosoftOfficeWeb 5.0_Pub?

I’ve spent two days tearing my hair out trying to get a rewrite rule to work in my web.config. It’s a standard rule I’ve written and use for a number of sites, it just won’t work on this one:

I’ve tried a thousand variations of:

            <rule name="landingpage" enabled="true" stopProcessing="true">
                <match url="^([_0-9a-z-]+)" />
                <conditions logicalGrouping="MatchAny">					
                    <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
                </conditions>
                <action type="Rewrite" url="landing-page.php?q={R:1}" />
            </rule>

Nothing. Then I noticed something. All the other sites are on IIS/7.0. This one site - MicrosoftOfficeWeb 5.0_Pub
So far, I’ve not found anything on Google on how to get the above to work on whatever MicrosoftOfficeWeb 5.0_Pub is…

It’s a .net site, but I need the rule above to take care of any “friendly” urls ( mysite.com/anything-goes-here ) and send those over to the php page defined in the rule.
No matter what I do - I get “page not found”. I’ve not found a way to see any debug info either so I can see exactly WHAT 'page not found" it’s looking for either.

Ideas? I’m currently stuck