about the passwd in the database

[Lee Bobby]

hello,everyone, 
   I am trying to write a NAS software which is located in the user PC.But 
now,I meet problems: 
   I have read some codes of freeradius-0.9.3,and find that on the SERVER 
the user-passwd is make out of the MD5 digest.I also find that the server 
use the real user-passwd from the database to compare with the user-passwd 
from the RADISU packet. 
   Any one can help me to resolve the problem? Why the user-passwd is 
turned into real passwd which is used to compare with the passwd from the 
database? 
   Thank you for all reading my poor English. 
regards