Hello,
you can just add a new OS DC to the domain and no real migration is required. Details are in:
http://msmvps.com/blogs/mweber/archive/2010/02/06/upgrading-an-active-directory-domain-from-windows-server-2000-to-windows-server-2008-or-windows-server-2008-r2.aspx
Important is that DC/domain are healthy BEFORE starting.
Con: NONE
PRO: Windows 2000 is out of support, functionality like Fine grained password policies, lot more GPOs and so much more as that is a major jump for the OS version.
Best regards
Meinolf Weber
MVP, MCP, MCTS
Microsoft MVP - Directory Services
My Blog: http://msmvps.com/blogs/mweber/
Disclaimer: This posting is provided AS IS with no warranties or guarantees and confers no rights.