This
other discussion might help you to get started since it has a few good resources.
You don't really need an editor for SOAP since it is not a language by itself. SOAP is a specification built over XML and so you will implement SOAP
using XML. Any standard XML editor should be good.
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Ajith Kallambella M. Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.