<p>Working on implementing TFS throughout our organization.  It is easy to integrate with <code>.NET</code> projects and any platform that uses Eclipse or a derivative of Eclipse for editing.<br>
What's the best way to use TFS version control with Xcode (now that I find out we need to write some iPhone apps)?</p>

One way would be to use the Team Foundation System client under Windows in VMWare, and check out (or whatever TFS calls it) your sources to a directory on your Mac that's shared with the virtual machine.  It also looks like
Teamprise
has a Team Foundation client for Mac OS X built atop Eclipse that would be worth looking into.
That said, I'd very strongly encourage you to use a
natively
cross-platform source code management system like Subversion or Perforce instead of a platform-specific silo like Team Foundation System for your company's soruce code, especially since you're going to be doing multi-platform development.
While you're not likely to share code between a .NET application and an iPhone application, having full cross-platform access to things like design documents can be really important.  Mac OS X 10.5 and later include Subversion, Perforce is readily available, and both Perforce and Subversion are natively supported by the Xcode IDE.  Subversion in particular is also more likely to be familiar to experienced Mac and iPhone developers you might bring onto your projects as you ramp up.