MD5 Encryption!! Help!

Okay heres my problem.....

I have in my Database Username/Password fields. The password field stores the users password md5 encrypted. I would really like to keep the data stored in the field encrypted with md5 encryption.

I am receiving from a client(i can't change how the client behaves) a username and (timestamp+password md5 encrypted) this is just like the APOP command for the pop protocol.
http://www.faqs.org/rfcs/rfc1939.html

We both know the timestamp...

Heres a session example:
S: +OK POP3 server ready <[email protected]>
C: APOP username c4c9334bac560ecc979e58001b3e22fb

So the client is sending back MD5(<[email protected]>tanstaaf) with tanstaaf being their password.

I can query my database for the username and get their md5 encrypted password, thats no problem...but how to compare it to the plain text + timestamp then md5encrypted password..??


MD5(timestamp + password) ~ MD5(password)
I already know part of the text used for one md5 encryption and i know what the password encrypts to in md5...there must be a way to put these two things together...? I'm not looking for clear text to anything, I just need to see if the hashes can be compared somehow.

For example can I do something like this?
MD5(timestamp + password) ~ MD5(password) + MD5(timestamp)

NOTE: I do not know the clear text of the password, I only put MD5(password) to make it easy to read, I only know the MD5 hash of the password.


Thanks guys,
Mitchel


p.s. I posted this in C# forum because I'm developing the software in C# but it's not really about the C# language.