Passwd format?

The Handbook and crypt(3) say passwords in master.passwd are MD5 hashes 
if they start with $1$, for example:

$1$DP.s8oCc$VJo0/026/S5ng6HlD1Sz8/

the format is $1$salt$rest. I have several questions:

How are the values encoded? This looks something like base64.

Is it possible to actually verify the password against this format using 
only a bare implementation of the md5 algorithm?

Actually, the reason for these questions is that I'm considering using 
LDAP authentication on a machine with lots of users and I'm wondering if 
existing passwd information could be transported to LDAP. Any 
experiences/docs on this?

Thanks!