Manually generate encrypted password

 I would like to manually generate an encrypted password so I can compare it with an encrypted password that was generated by ASP.NET's membership methods.
Here's the deal, I have an old application that used ASP.NET membership provider.  I have a new app that also uses it's own distinct implementation of the membership provider in it's own database.  I would like to check if the person logging into the new app for the first time has the correct username/password combo for the old app. 

I would like to take the password and encrypt it in the same manner that the ASP.NET membership provider does so I can manually compare it with the encrypted password in the old database.
Any Ideas?
 
Details:  the old app specifies the validationKey & encryptionKey explicitly, specifies decryption="3DES"  and validation="SHA1" in the web.config machine key.  It also specifies password ...