[:D] All I can say is WOW!
Virtual PC 2004 is a truly awesome program and has become this BizTalk developer's best friend. In the past I'd always setup a new development workstation when doing beta testing, trying pre-release software, etc. but recently a friend suggested I try Virtual PC instead. If you're not familiar with the technology, VPC allows you to host other "guest" operating systems such as Windows Server 2003 for use as a development platform. For BizTalk Server 2004 (and soon to be 2006) developer's, running under Win2K3 is a must for "full-featured" development including HWS, BAS and the SharePoint Adapter.
A few words of caution.
1. Make sure you have a fast "host" machine with plenty of RAM. I'm currently running on a Dell Inspiron 8600 notebook with 2 GB system RAM.
2. Download and install the latest VPC Service Pack (SP1). Everything runs much smoother. Also, install the "VM Additions" for the best performance and user experience.