When I am designing normal Java project in Eclipse, I can add predefined libraries to it's Build Path. Can I do the same way when putting jars into WEB-INF/lib folder of Web project? I.e. can I ask Eclipse to put some predefined library jars there?
Just copy / import a Jar there; it will be added to the build path automatically. You will find it in the package explorer within the Web App Libraries (or in the build path in the project properties). The project has to have the Dynamic Web App nature.