Installing JPL

For installing JPL, I proceed as adviced here

http://www.swi-prolog.org/packages/jpl/installation.html

but I get the following errors while trying to execute the Java
examples:

'plcon.exe' is not recognized as an internal or external command,
operable program or batch file.
....
package jpl does not exist
....

although I have made all the path and classpath modifications and put
jpl.jar in my path.
Please help me,
Monica
.