Thomas,
The catalog is used to enter in local references for DTDs and Schemas, the entry you pasted above doesn’t buy you anything since the parser will still go out to the web and try and resolve the DTD. Whta I suggest you do is download the DTD and change the URI to something like: file:/c:/dtds/spring-beans.dtd
That way you don’t need to worry about the proxy settings and instead of the local copy of the DTD will be used.
However I would note that there is currently a bug in the catalog that doesn’t allow editing or deleting of user entries, we hope to address it soon.