How to set up a test environment

When setting up a test environment, what process do you follow? How is this process different for the Web?

For the most part, I don't set up test environments anymore and I recommend against test teams installing and configuring systems under test -- unless the end user is expected to install and configure the system on their local machine.
The key to test environments is that they should be as similar as possible to production environments (in most cases). It makes no sense to me for someone to expect the test team to be able to install and configure an application on machines that don't match production (or the development environment for that matter) when the test team wasn't even involved in figuring out how to install and configure the system the first time. Whoever is installing and configuring the development and production environments should be installing and configuring the test environment.
If you are asking about setting up a test lab to test application compatibility across various platforms, browsers, etc., I've become a huge fan of virtual environments.
If you are asking about testing support environments (defect tracking systems, automation tools, requirements management systems, test management systems and so forth), that is entirely dependent on your corporate policies, project goals and the tools your team uses.