Don't get me started on Project...  OK.  Get me started...  I hate how MS Project refers to People, your TEAM, as "Resources".  :-(  However, I'll keep my mouth shut, since I want to mention a one thing related to Team System.

First, if you're entering work items in Project you'll have to enter the "Resource" name as a string, and you won't have a drop down to select from (until you have entered the name at least once).  This is in contrast to Excel, where you get a drop down of all the available people to assign the task to.  It's frustrating, but there's a reason.  Project supports assigning multiple "resources" to a task, while TFS supports only one person on the Assigned To line (by default).