Is it the CLASSPATH you're trying to set, or the PATH? What are you doing, and what errors are you getting?
Setting the PATH variable allows you "to conveniently run the JDK executables (javac.exe, java.exe, javadoc.exe, etc.) from any directory without having to type the full path of the command." To set the PATH, see these installation instructions for 32-bit Windows. (For other operating systems, click here.)
Setting the CLASSPATH variable "tells JDK tools and applications where to find third-party and user-defined classes." To set the CLASSPATH, see these JavaRanch instructions or Sun instructions. [ January 04, 2006: Message edited by: marc weber ]
"We're kind of on the level of crossword puzzle writers... And no one ever goes to them and gives them an award." ~Joe Strummer sscce.org
If you are posting in this forum, then you should NOT use the CLASSPATH variable AT ALL. You should delete it completely.
If that still does not fix the problems you have encountered, please describe what you are doing and what error messages you get. These details will help us fix your exact problem rather than wasting your time with out best guesses.