That very much depends on type of analysis or (obviously)size of model.
However:
Memory: Enough to have operating system, N4W and model in memory simultaniously, 1 GB or more
Harddrive: SCSI 320, big enough but no need to overdo it. Obviously: very much depending on model size.
Clock speed: The old "the higher the better" applies.
If you are looking for "cost effective" I think memory gives more value than clockspeed. Higher clockspeed often means "new computer" while adding memory is simpler and cheaper.
A tip: Use Windows Performance-monitor in the "administrative tools" menu to find the bottle-neck in the system.
Good Luck