You are mixing some concepts.

Team foundation is server software for managing projects, with features like
sharepoint integration, reporting services, testing results, automated
builds, keep control of tasks, bugs and so on (with work items), people in
the project, requirements, etc. and it is separate of Team System visual
studio versions, but works in tought contect with them.

Team system visual studio editions, are different "flavours" of the visual
studio 2005 client IDE to use alone or in contact with Team Foundation, and
depending on the flavour, it has some features like system designers (in
architecture versions), unit testing, class diagrams (in developer versions),
and web and load testing in tester editions.

You can find more info about Team system here:
http://msdn.microsoft.com/vstudio/teamsystem/

and about Team Foundation here:
http://msdn.microsoft.com/vstudio/teamsystem/team/

I hope it will help you