This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Yes you can install multiple database products on one machine because they usually use different ports to allow client connections. I have MySQL and PostgreSQL installed on most of my systems, and in one case also have SQL Server.