I took me a couple of hours of research, waiting and clicking, but I have successfully been able to install the public beta of Sharepoint 2010 with the SQL Server 2008 R2 November CTP with PowerPivot for Sharepoint Server 2010 on a single VM.
This is the proof:
While I have been recording my installations steps, I will not put them here, as I came across another post that describes the required steps in even more detail, including the solution to my broken setup.
A big thanks to Vidalis for posting the required installation steps:
Everything is public Beta material, so you can give it a go yourself!
I downloaded and installed Sun VirtualBox : I use this to host the 64-bit guest on my Windows 7 laptop. Alternatives are Windows Server 2008 with Hyper-V or VMware.
I recommend assigning at least 2GB to the VM, although 4GB is the recommend minimum for Sharepoint. When creating the VM, choose Windows 7 64-bit, as there is no separate option for Windows Server 2008 R2 yet.