Dual Processor On G5 And Photoshop


I'm using Photoshop CS on a dual processor G5 and finding that it is having trouble (=crashing) with some operations (scale and rotate) on large 16 bit documents.

I am something of a newbie but have discovered that one issue might be that I should have more than one scratch disk to take advantage of the dual processor. Is there anything I could/should do to allocate Photoshop between the dual processors- or does G5 do this automatically?

Thanks in advance