migrate security from ASP to ASP.NET

I am stumped on this issue. I have an old ASP environment where users are authenticated against an existing Oracle database. Now I am trying to add new web apps in ASP.NET using VS2010 in vb. Particularly, in existing authentication I have following statements (as part of a big include files with many reusable code):
Set pwd = Server.CreateObject("DecryptOraDB.DecryptPassword")
and in SQL command this pwd is used in where condition which looks like this:
tblusraccounts.password='" & pwd.DeCrypt(CStr(p)) & "'
Just FYI: The table tblusraccounts holds all required firsname, lastname, username, password,etc. I have successfully connected to Oracle database using OracleConnecton and hardcoded specific username and pwd. But I need to be able to verify other users using usrname & password for new app and I cannot find any help how to convert the above two statements in asp.net so that I can use existing DeCrypt method in ...