I\'m currently experimenting with build script, and since I have an ASP.net Web Part under source control, my build script should do that at the end:
With VMWare, there is the Virtual Machine Automation APIs (VIX API). You can find the reference guide here. It works with VMWare Server and WorkStation, but AFAIK it's not available for ESX Server.
From the main page for VIX:
The VIX API allows you to write scripts and programs that automate virtual machine operations. The API is high-level, easy to use, and practical for both script writers and application programmers. It runs on VMware Server and Workstation products, both Windows and Linux. Bindings are provided for C, Perl, and COM (Visual Basic, VBscript, C#).