How to retrive userid

Question

I have a login screen like this.

In this login screen record get inserted into aspnet_membership table of sql server. UserName and password get stored to this table in encrypted form. I want to retrive Userneme each time when user login with his userid and password and get stored into my different master tables. So problem is that how I can retrive UserName from login screen and get stored into another database tables as UserID?