owssvr.dll can be used in InfoPath projects to provide filtered or cascading drop down lists. Use an XML datasource - the syntax is http://yourserver/yourweb/_vti_bin/owssvr.dll?Cmd=Display&List={guid}&XMLDATA=TRUE.

However, beware if your list contains a lookupfield that allows multiple selections. If you have this, then the above syntax will return an invalid XML, or a blank data set.

List contains lookup field(s) with single selection - syntax works.
List contains lookup field(s) with multiple selection - syntax fails.