Sharepoint SSO to SAP Portal

Hello,

I would like to know if there is any step by step implementation guide or blogs that describes how to implement SSO between Sharepoint 2007 and SAP Netweaver Portal.

We already have Windows AD authentication for our Sharepoint site and would like to leverage that for logging onto the Portal. So when the user is authenticated from once for Sharepoint and they click on a link to the EP website it should ask for user id and password again.

I have been reading documents on using SPNego module, Kerberos ticket based single-sign-on etc but am confused which is the right method to use.

Please help.

Thanks