Digital BW, The Print

I'm using an Epson 1280 with Photoshop Mac OS X or 9, MIS VM inks and
am having the posterization problem I've often read about on this
group in the darktones.  I've tried both Paul and Tyler's curves.  It
seems as though only the PC users have been able to get the 1290
driver to work to fix this problem.  Is this true?  Is there any easy
way to get my mac to believe my 1280 is a 1290 so I can print
adequately?

I'm kinda bummed cause I just got started and already worried I might
have a systemic problem printing high-quality with the 1280 driver. 
Any help anyone can give would be greatly appreciated.  Thank you.

-Murph