Maybe it's not so fresh information but it's worth mention here as TFS users would read this.
Microsoft released fully configured virtual machine images with Team Foundation Server 2008 installed. There are two images: one with Visual Studio 2008 and one without it.
After running you will have the possibility to play with all features as everything is configured and just works. For example you can test new build features and compare it to your current installation.
One disadvantage is that you will not be able to install Team System Web Access because of policy setting that will prevent you doing so. But you can still install it on different machine and point to your test server.
One thing you should remember is that these machines are for evaluation purposes only and will expire April 1, 2008.
You can download if from the Visual Studio 2008 Trial page.
You must have either Virtual PC 2007 or Virtual Server 2005 R2 SP1 installed to run these virtual machines.