Digital BW, The Print

Hello kind souls.
I hope you can help me with a problem neither Epson nor Adobe can help me with.

I'm on a Powerbook G4 with 1GB ram, 15GB free on internal HD and 152GB free on 
external HD.   Use Photoshop CS.  Run OS 10.3.3.

Have had recurring problem with incomplete prints.  Often, but not always, on large files, 
printer prints 1/4 or 1/2 of the image, then spits the rest out blank.

I've received advice on changing memory allocation.
Epson told me to radically increase memory to Photshop (in Photoshop/Preferences/
Memory) - OS 10 does not allow memory changes.

Problem persisted.
Others said, no, take memory for Photshop back down to 45 to 65 % and change my 
primary scratch disk to my external hard drive which has so much free space.

I did that. Seemed to improve.  Got two large 13x19's and one 8x10 printed.. but on 
second 8x10, i got only 1/4 of my image again.

I would welcome any of your advice.  A friend recommended this forum as hosting a 
wealth of kind hearted, knowledgeable people!