Starting with a Windows 2003 base image I installed SQL 2005 (had intended to put 2008 on as well but the machine was not of my making originally so ran out of space), CRM 4.0, VS2008 and the CRM SDK. Once my next project is up and running with it I will also look at putting the Analytics accelerator onto the base reusable image.
I suppose my main difficulty was not with the technology but the platform. Taking a pre-installed domain controller with Exchange was a step up but found that I had to take SQL off and re-install to my own preference (while adding SSRS/SSAS as well). But mainly I struggled against the VM. Capturing ISO images of VS that it said was corrupt one minute but fine the next, occasionally dropping the USB connection to the external HDD where the image is located and loosing work. Still - at least I have had a lifetime of practice at installing CRM now!!!!