The answer to the first question is no. PropertyPlaceholderConfigurer was not designed to load xml files, it only works with standard java property files. The reason for that is simple: xml involves logic in the specification of properties (for example in your case it is logic that a car has a type or a colour) so an xml parser extrapolating that properties cannot be done to be "general": it has to be specific.
Since Spring is open source, you could open the PropertyPlaceholderConfigurer class and learn how it works, and then maybe extend it or write something similar, that can understand your specific xml property file.
For the second question, yes, you can put properties file wherever you want, even in external jars, as long as the jar or the path IS on the classpath of the application. To access the correct package, simply use the standard package "Unix-style" navigation: