problem in verifying MD5 decrypted passwd with plain text one

[kavita <kavita@worldgatein.net>]

hi everybody,
       am adding entries of users in a ldap and providing a web-based
link for change their password.
i have a detailed entry of users in a ldap like
username,password,mailquota,uid,gid etc.
user's password is stored in MD5 base64 encrypted format.
as all change password script requires old(current) password for
verification of valid user and then new password and confirm (re-type )
password. 
when i retrieve user's old(current) password it is already decrypted.
now i want to match this decrypted password with plain text password
which is entered by use(current pass).

how shall i do it?

Thanx in Advance.
-- 
Kavita Modi
S/W Engg.
Worldgate Network Private Limited.
206,Trividh,
Ring Road,
Surat - 395002.
E-Mail:kavita@worldgatein.net