To the best of my knowledge, there is no multipath software for Linux yet. The current implementations available for Windows and commercial Unixes cost quite a bit and I suppose there is resistance in the Linux comminity to use licensed, and quite expensive, software.
However, the demand for such software with Linux support is growing, and I do know there will be a version of HP/Compaq's implementation of a multipath driver (SecurePath) available for Linux perhaps this year. This will however be coupled with StorageWorks storage subsystems and will most likely not be supported with a generic brand of storage.
/charles