No lo he probado nunca, pero aquí está:
http://java.sun.com/j2se/1.5.0/docs/...html#resources Cita: A nativelib element specifies a JAR file that contains native libraries. For example:
<nativelib href="lib/windows/corelib.jar"/>
The JNLP client must ensure that each file entry in the root directory of the JAR file (i.e., /) can be loaded into the running process using the System.loadLibrary method. Each entry must contain a platform-dependent shared library with the correct naming convention, e.g., *.dll on Windows or lib*.so on Solaris/Linux. The application is responsible for doing the actual call to System.loadLibrary.
Native libraries would typically be included in a resources element that is geared toward a particular operating system and architecture. For example:
<resources os="SunOS" arch="sparc">
<nativelib href="lib/solaris/corelibs.jar"/>
</resource>
By default, jar and nativelib resources will be downloaded eagerly, i.e., they are downloaded and available locally to the JVM running the application before the application is launched. The jar and nativelib elements also allow a resource to be specified as lazy. This means the resource does not have to be downloaded onto the client system before the application is launched.
Parece que lo que hay que hacer es meterla dentro de un jar, pero supongo que unicamente por compresion y nomenclatura. No lo he probado nunca.