Invisible class files inside jar archives

Hi!
After developing an application with J2SE 1.4.1_05, under Windows 98, using some packages archived in jar files, I cannot launch the application with the J2RE 1.4.2_02 or J2SE 1.4.2_02 (in the same Windows 98) because the class files in the jars are not 'visible', even if the CLASSPATH is set up correctly. The only classes that work right are the unpacked ones. But it still does work in Windows 2000.
What might be wrong?

Thank you for your answer, and excuse me if my question was kind of confusing.
The issue here is that the files ARE in the jar files (without './' on the front), but in the environment (Windows 98 + J2RE 1.4.2_02) the application does not work, unless I unpack the jars and use the packages in the same manner I did during the development stage (for example, all classes of package 'myutils' in the folder 'myutils').
The weird thing is that this DOES NOT happen in the environment (Windows 2000 + J2RE 1.4.2_02)!!! Just after installing the J2RE 1.4.2_02 under Win2K, the app does work OK! That is why it seems that ONLY in the first case (Windows 98 + J2RE 1.4.2_02) the class files inside the jars seem to be 'invisible' to the environment.
As I have mentioned in my question, the app was developed in the environment (Windows 98 + J2RE 1.4.1_05), and it did still work with the jar files, so I wonder if there might be some compatibility between Windows 98 and the J2RE 1.4.2_02.
Except my own jars, the same thing does happen with the jai_core.jar file coming with JAI 1.1.2. But this does not happen when it comes about rt.jar, in ..\jre\bin!!!
All in all, the question still is: what might be wrong?

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