Remote Desktop Services (formally Terminal Services) has dramatically improved and matured starting with the Windows 2008 launch.  In many ways, it allows Citrix installations to be replaced by native Windows technologies.

You can read more here: http://microsoft.com/rds

This week Microsoft released a very nice diagram/poster of the technology.  Check it out here:

http://www.microsoft.com/downloads/details.aspx?FamilyID=9BC943B7-07C5-4335-9DF9-20E77ED5032E&displaylang=en