Sorry for the bump, but I've been having a problem almost exactly like the OP.
I'm trying to open some .tiffs in photoshop CS4 which are between 400Mb and 1Gb and getting that same "not enough memory" error.
I'm on a windows xp machine, so I'm not sure that all of the methods outlined here are applicable, but I've completely disabled OpenGL, and my scratch drive is 980GB. (I could use the C drive and have 258GB if that would be better) I've maximized the RAM that photoshop has access to, but despite the fact that I've got 3326MB RAM, Photoshop sees only 1689MB of it. History States is at 20, and Cache Levels is at 4.
I couldn't find where to disable the Version cue, and the plugins for photoshop CS4 seem to be different than CS3, so I left those alone as well.
Any help at all would be appreciated.