EXS 24 Logic Sampler Users Group

Has anyone figured out what the most efficient Mac/HD system for getting the
most out of EXS24 mkII is?  I'm not happy with the performance of my system.
I'm using the following gear:

Mac dual 450 G4 with 1 gb of memory.  I have an IBM 7200rpm Ultrastar drive
mounted internally and partitioned into 2 40-gb volumes as a secondary
internal drive.    

I have 2 external 120 gb WD caviar 7200 rpm drives mounted in firewire
enclosures which have all of my EXS intruments and associated audio files,
with aliases of all this in my Logic Audio folder on my boot drive
(factory-installed 30-gb Quantum Fireball--not sure what speed it runs at).

Running Logic Audio 6.1 using the "mac" Audio driver, and TDM.  I have an
old PT 24 system with an extra farm card.

I don't think I'm getting the performance I could.  I get system overload
messages quite frequently!  Every day, I wonder what I need to do in order
to get real performance from these incredible software tools--currently
hampered by lethargic hardware.

TC