Summary: docx4j can convert WMF files to SVG using pure Java approach.
Note regarding options for converting WMF files to SVG and/or PNG
(as at Feb 2010):
wmf2tosvg is a good solution for WMF (although it has no EMF support).
For WMF, we'll use it. This can be revisited if/when com.adobe.dp.office
(EMF is the real problem - see note in MetafileEmfPart)
Batik has WMFTranscoder, but not EMFTranscoder! Even if it did,
Batik is best avoided as it is no good on appengine since it uses
awt, and spawns threads.
imagemagick does a nice job with WMF, but has no support for EMF at all
(other than on Windows). So given that we are stuck with a partial
solution, its best to use pure Java.
For completeness, a note that openoffice can be used to convert EMF
and WMF; I found it worked well.