Hello,
Will your hardware allow upgrading from RHEL 3 to 4 on the same server, if 
so, i would do that first and then upgrade Networker versions.
If not You can dedicate a new RHEL 4 server and do a host transfer ( 
Licence transfer ) to the new host id.
You should have complete backup and fail over plan before doing so and 
make sure your maintenance is upto date so that updates\enablers if 
required are readily available from EMC.
It would also help to go over compatibility matrix for RHEL4, Devices, RPM 
etc.
HTH

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