Membership Information from Stored Procedure

Hi all, I'm trying to do something that seems so simple, yet I'm having a tough time finding the solution. All I want to do is determine the ASPNET userID from the Membership database created by ASP.net using a stored procedure. My SP is trying to insert information to a table and one of the fields is the userID (which I need to get based on who's logged in). Any help would be greatly appreciated. Thanks, Tim ...