ahead: currently OS X makes better use of available RAM than XP under the same preconditions, although i still don't find it very intuitive how one could max out memory usage on a say 8GB G5 (see the other threads about memory usage)
DAP is currently only available for plugins (everything what profits from expanding CPU power) and looking at the principle in detail makes it clear why any kind of sample streaming will be more complicated.
an audio-track on machine A needs some processing, so you send the audiostream (via gigabit-network) to a slave and tell a remote application to do something with the incoming data and send it back - finished, easy.
when it comes to sampling one needs to have a plugin loaded (be it exs or a vienna instruments player) which needs to know a patch to be loaded, receiving midi-data, stream the samples from a harddrive and send audio back (obviously it would make minor sense to stream the samples also across network and so eat up bandwidth, add latency, ect).
such a procedure would be much more sophisticated because the core application would need to know many details from the slave and eg. hinge itself deeply into the filesystem and memory management of the remote machine.
i don't say it would be impossible, but currently it is not designed that way.
but of course you could have an additional copy of logic running on the second machine, load instruments there and access it from the core machine, even route the resulting audio back and access such a *headless slave* via apple remote desktop.
christian