We are about to setup a cruise control.net with and NAnt and TFS, do I need visual studio 2005/2008 with team explorer installed or can I make this work with just the free Team explorer client
Team Explorer will install the VS shell, which gives it enough of VS to operate.
So strictly the answer is "yes, Team Explorer requires VS", but since VS is included in the Team Explorer install the strict answer is kind of unhelpful :-).
Once Team Explorer is installed, you get access to the TF.EXE command line tool, but also worth looking at the TFS Power Toys for the tftp.exe command line tool and the PowerShell Snapin for more command line operation.
All you need to get the CruiseControl.NET integration working with TFS is to install the Team Explorer download that you pointed to. This will install the API's necessary into the GAC for the plug-in to work.
Be sure to install the TFS 2008 Team Explorer as that includes the latest versions of the client assemblies that I compiled the latest version of the CC.NET plugin against.
Not to take this down a licensing rat-hole, but just wanted to note that the Team Explorer software isn't "free" as such, but is a freely available download. You need to make sure all your developers who check code in to TFS (and therefore might trigger an automated build) have TFS CAL's (Client Access Licenses). A TFS Cal is included with an MSDN Subscription that includes a Team Edition of Visual Studio or they can be purchased separately.
Good luck!
Martin.