Thanks, this Object does the trick for IIS6.
For IIS7:
I did the client certificate mapping based on this script:
http://blogs.iis.net/ulad/archive/2007/01/19/vbscript-to-configure-one-to-one-client-certificate-mapping-on-iis7.aspx
And enabled Ssl, Ssl128, SslRequireCert,SslNegotiateCert and anonymous access. "system.webServer/security/authentication/iisClientCertificateMappingAuthentication" is also enabled, the module is installed.
But when I access the site the mapping does not occur, but I'm asked for a client certificate. I'm still the anonymous user. So the client certificate must be valid.
-- Edit: Solved:
I installed the mappings in a vdir instead of the WebSite itself (eg. "Default Web Site"). Now, installed at "/", it seems to work.