Try putting you counter class in a package.
So, in the first line of your counter.java class, you would have a
line like:
package beans;
public class counter ...
(You should arrange source files in a directory tree that reflects
their package tree. In case you've never worked with packages before,
when you compile counter.java, you have to have it in a directory
called "beans". Run the javac compiler in the directory just above
the beans directory.
e.g. javac beans\counter.java)
Then create a directory called beans in the classes directory. Put
the compiled class file in the directory:
F:\jakarta-tomcat-5.0.24\webapps\ROOT\WEB-INF\classes\beans\
Finally,
change your jsp to the following:
...
<@page language="java" import="beans.counter" />
<jsp:useBean id="test" class="beans.counter" />
...
Of course, you can name the package anything you like.
Honestly, I'm not exactly sure why it can't find your class, but this
should work - and packages are actually common practice anyway.
See if this works for you.