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I've tested in XP64 (crusty install) on a GeForce 9600GT 256MB (180.48), and on an old machine with a new XP install and a GeForce 6600GT. (Both in CS3, but I doubt the version will make any difference.)

I've updated (r39) with a few changes, including a check for software rendering (it'll just throw up an error).

If it doesn't work, hold down left-control-shift when you select the plugin, and it'll open the diagnostics console window when the plugin starts. (Don't try to close that window--it'll crash Photoshop.) Check that the vendor and renderer outputs look correct; they should be "nVidia Corporation" and your video card.

Also reduced memory usage a bit more; 10000x8000 done in about 1.1 gigs. (It'll always be more than the commandline, since Photoshop always wants to keep extra copies for undo, history, etc., but it should be low enough now to not matter. If you're trying to edit images that size, you really need more than a gig of RAM...)