reporting services internet authentication

I have Server2003/SQL2000/IIS6 and have just installed Reporting services. I have two websites on the server. Access to reports is fine using the http://servername/reportServer, and using IUSR_servername, but I would like to have reports available via the Internet using domain names. Saw the earlier post and read I needed to change configuration. I've tried:

<Configuration>
<UI>
<ReportServerUrl>http://servername/ReportServer</ReportServerUrl>
<ReportServerExternalURL>http://www.domain.org/ReportServer</ReportServerExternalURL>
</UI>

and

I've added virtual directories under above domain for reportManager and reportServer giving appropriate read/execute permissions and security under IIS.

I continue to get: HTTP Error 403 - Forbidden

Can I do this?
And, is it possible to have both domains access the reportServer and not just one?

Thanks so much