Martin Woodward has a posted a great set of slides from a presentation he did on what's new in TFS 2008. After going through all of the features other than build, he spends more than half of the slides on the build features of TFS 2008 (aka Team Build). I highly recommend taking a look at the slides, particularly if you haven't paid close attention to TFS 2008 up to this point.
Last night I had the pleasure of presenting to my local .NET User Group (NIMTUG) on what is new in Team Foundation Server 2008. Interestingly, most of the audience where new to TFS completely so I also covered a bit of ground on what Team Foundation Server did and why - however most of the talk concentrated on the Team Build stuff new in TFS 2008 and I ran through the wallboard demo that I wrote for TechEd.
One of the slides shows a condensed diagram of the new object model for build in TFS 2008. I've copied it here (you may need to make your browser wider to see the whole thing). It does a great job of highlighting the central parts.