Do not waste your time with 5.2 on W2K, won't work. Many have been down that road only to hit a head end. 5.1 might work on W2K, I've heard it works, BUT YOU WILL BE RUNNING IN AN UNSUPPORTED CONFIGURATION!!!
If you have to use Winblows, to be supported by Sun you have to use NT. I believe both 5.1 and 5.2 are supported on NT.
As for mailing lists, you do not need an API. Mailing lists in iMS are not like lists served by Majordomo or MLM. First I'd decide what kind of mailing lists you desire. iMS lists are controlled via LDAP, so all you need is ./ldapmodify.
-Chad-