In Eclipse, press Ctrl + Shift + O to organize your imports. This will look for all unknown classes on the classpath and try to import them. You can also place your cursor on a class name and press Ctrl + Shift + M to attempt to import that single class. This is sometimes helpful for class name collision (i.e. if two packages have a HttpClient class, you can click on the desired class).
If the jars are in Referenced Libraries, then they should be on your classpath. You can verify this by right clicking the project and selecting something like Build Path > Configure Build Path, then click the libraries tab.
Also, you probably have build automatically selected by default, but if you don't, you'll need to build your project. You may also want to attempt to clear the build path and re-build it. I've seen my Eclipse get out of synch a few times and this fixed it, albeit somewhat of a fluke.
If you're using Maven, this sort of thing can sometimes occur if you have an incorrect dependency scope (i.e. runtime, or test vs. compile).
For what it's worth, unless you're utilizing the entire package, there is no reason to import an entire package's contents (i.e. import package.*).