How to solve plug-in install problem during ORACLE Migration Workbench installation?

I am installing Oracle Migration workbench (10.1.0.4.0), want to migration data from SQL Server 2000 to Oracle. I downloaded omwb.zip file and sqlserver2k.zip plug-in. I put the plug-in in “plugins” folder during the installation, renamed it as SQLSERVER2K.JAR, and unzip it there, the unzip process generated two folders: META-INF and Oracle in the "plugins" folder. There is a MANIFEST.MF file in META-INF folder, and in oracle folder, several small folders folder with a lot of .class files. I started the OMWB.BAT file in bin folder, I still get the error information: “No okugubs are installed. Please install…. “.

I tried many times, including rebooted the machine and restarted the OMWB.bat ifle, but still got the same error message.Could anyone who installed the OMWB before and know how to solved the plug-in problems help me?

I am thinking: do I need to put all of the .class files in the folders into the “plugins” folder directly?

Thank you very much for your help.