Not enough RAM for Optimized JPEG

I have a 440MB native .psd file (flattened & CMYK) that triggers this error message when I try to save it as a Maximum quality JPEG file in PS CS2: "Could not save as (filename.jpg) because there is not enough memory (RAM). Try saving without optimization or as a baseline JPEG."

I am able to save it as a baseline JPEG, but does anyone know what is "optimized" about the color in an optimized JPEG? The two lines below are from PS CS2 Help:

Baseline (“Standard”) Uses a format recognized by most web browsers. Baseline Optimized Creates a file with optimized color and a slightly smaller file size.

A second concern is why there isn't enough RAM in the first place. How much does it take, and why isn't disk space being used even if RAM runs out? I have a dual G5 with 4GB of RAM and about 100GB of available disk space. I'm running OS X 10.4.8. Activity Monitor shows I'm using just over 1GB of physical RAM for Photoshope and under 500 MB for all other open processes.

Try change preferences to [enable large document format (.psb).] regards Bj.

I serioulsy doubt that PSB enabling would make a difference, it just adds the choice of that file format.

Rick, what do you want to do with that JPEG? JPEG and CMYK are not usually good friends, maybe this is a limitation or a bug. Have you tried creating a CMYK optimized JPEG from a small file?
And could others try to save such a file? (huge CMYK>Optimized JPEG)