fs hardware configuration

I'm finally going to build a proper fileserver.  I have a PC with
512MB of memory, symbios scsi controller and 2×9GB SCSI drives.  I'm
also getting 2×120GB IDE drives.  My limited understand leads me to
believe that I could designate the IDE drives as WORM and the SCSI
drives+memory as cache.  What is the best way to configure this?

Also, are the idefs changes (dorman/geoff/nemo) in the latest
distribution?