Thomas Higgins has written 3 articles for SitePoint.
Implementing Your Own IaaS Solution
Implementing IaaS solutions can be a bit more difficult than first expected. Even known concerns have hidden surprises ready for the unwary.
IaaS in depth
Cloud computing - Infrastructure as a service
Virtualization and “As a Service” Platforms Defined
What is Virtualization? PaaS (Platform as a Service) vs. SaaS (Software as a Service).