Yes, I ahve experience with custom delegation in Windows 2003. Unless you are an extremely experience AD engineer, I highly recommend that you use a third-party security rights delegation product. Quest Active Roles is heavily used for this in Fortune 1000 organizations.
I'd advise you to pick up Bill Boswell's white papers on Identity Management available at:
http://wm.quest.com/reg/marketing/promos/whitepapers/identitymgmt/welcome.asp
All of the extended rights for delegation are listed here:
http://www.microsoft.com/technet/scriptcenter/topics/security/allrights.mspx
You can also read more about this subject at:
http://cc.realtimepublishers.com/portal.aspx?pubid=289
With Excahnge 2000, most mailbox quotas are set by system policies; thus, your user would need Exchange System Administrator rights.
To correctly configure Active Directory for a Delegated Authority Model based on a role Based Access Control is a complex task and requires a deep understanding of both the schema and how rights are applied in Active Directory. Consultants in the AD security field in North America easily make over a $100,000 per year, as there are simply not enough engineers with the speciality. Recently Microsoft was advertising for Ad Security Engineers with RBAC experience starting at $150,000 per year plus benefits.
