samba - Jul 2003 - Linux platform

Dear All,
 
I am planning a solution about migrate from Windows platform to Linux platform.
But I don't have much experience about Linux, so I want to have opinion from
you about this planning.
 
The whole solution is include:
 
1) One linux server (samba) (Domain Controller)
2) One linux server (sendmail)
3) One windows 2003 server (SQL)
 
Is that I need to build openldap server ?
How to implement Single Sign-on ? including sendmail's email account.
 
 
Thanks for your help !
 
 
Tommy