What version are you using?
The "iPlanet" name is fairly old now (things got renamed to "Sun ONE", then "Sun Java"), which suggests you may have an old version. The current version is 6.0 and you should take a careful look at it before installing a significantly older version.
The documentation (for all the listed versions) is on http://docs.sun.com,
* then either use the search function,
* or go to "Browse Product Documentation", "Software" - "Identity Management", "Directory Server Enterprise Edition", "iPlanet Directory Server 5.0" (or whichever version), "iPlanet Directory Server 5.0 (Multi-Platform Editition)", then "iPlanet Directory Server 5.0 Installation Guide".
* or of these URLs should work:
** http://docs.sun.com/app/docs/doc/816-5602-10
** http://docs.sun.com/app/docs/prod/ip.dirsvr50~S1_ipDirectoryServer_50#hic
But definitely spend some time maneuvering around docs.sun.com. There is a wealth of information there and it doesn't take very long to learn the layout.
Sun Java System Directory Server Enterprise Edition 6.0 is fully supported on Windows 2003 and get be downloaded from
<http://www.sun.com/software/products/directory_srvr_ee/get.jsp>
You can get the Native packages (Windows MSI) or the Zip packaging (just unzip).
Regards
Ludovic.