Ney,
I’m sorry but you cannot currently create RPC/Encoded Web Services in MyEclipse. This is because MyEclipse uses the XFire Web services framekwork which has decided not to support RPC/Encoded as it is not WS-I compliant.
If the XFire framework adds RPC / Encoded support, you will see support for this in MyEclipse almost immediately.
Is there any particular reason you want to develop a new web service which is RPC / Encoded?