Check the article below on how to install it on D or any other drive.Also I would suggest you to upgrade to MR5.
SEP installs few components on all user and common files directory and they cannot be changed.
How to create a Symantec Endpoint Protection install package that will install to a different drive
http://service1.symantec.com/support/ent-security.nsf/docid/2007111308022348
Obtaining an upgrade or update for Symantec Endpoint Protection 11.x or Symantec Network Access Control 11.x
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007121216494948