We are in the process of setting up a FileMaker Server Advanced 11 installation. We will be using one or two virtual machines for this, depending on whether we set up the database server and web components on the same virtual machine or different virtual machines. Does anyone have any recommendations on what has worked for them: one or two machines, and choice of operating system (Server 2003, Server 2008, Server 2008r2, and 32-bit vs. 64-bit)?

Thank you in advance for your help.

Two machines will give you the best performance if you expect a lot of web traffic.

As to the OS: stick with what you are most familiar with. FMS doesn't take advantage of 64bit so there is very little to be gained from it and it does complicate installation a little.