Brian Keller has the scoop:
One of the things we have received great customer feedback on is the availability of Virtual PC environments containing the pre-releases of Visual Studio 2008 and Visual Studio Team System Code Name "Rosario." The VPC's are pre-configured to help speed the evaluation of these pre-releases without requiring an extensive setup process to get started. However, unless you have a fast and reliable Internet connection (or even if you do) the process of downloading these VPC's can be a bit grueling.
Read the whole thing for the instructions.
There's also the Microsoft Secure Content Downloader July CTP...I haven't tried it, but it looks interesting.
Brian Keller: Technical Evangelist for Team System : A More Reliable and Faster Download Experience for Rosario / VS08 VPC's