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.
I'm not sure if this was actually the question you wanted answered, but most available web servers do not support servlets as supplied. There are servlet extensions available for most of the big name servers (Apache, IIS, iPlanet ...), but they all need to be installed by a system administrator which may not be fasible if you are just renting web space on a public host. If you have control over the software and configuration of your web server, then you can choose a plug-in servlet extension which works with several web servers to be assured of at least basic compatibility. Resin, JRun and ServletExec seem fairly flexible about partnering with other web servers, others may be more specifically tailored to one server.