?Non Hi-res Powerbooks have 64MB of vram and do not support the higher res modes of the 128MB vram version.
I have one of these too, but I'm perfectly happy with the display limitation.

The non hi-res 17" powerbook is listed as having 128MB and still can't, apparently, produce resolutions beyond 2048x1536

> The non hi-res 17" powerbook [...] still can't, apparently, produce resolutions beyond 2048x1536

"The maximum resolution supported on an external display is 2560x1600 at millions of colors."
http://www.everymac.com/systems/apple/powerbook_g4/specs/powerbook_g4_1.67_17.html

> Non Hi-res Powerbooks have 64MB of vram

Apart from the non-hires 17" model with 128 MiB standard VRAM (as mentioned by ausPPC) there were also 128 MiB VRAM BTO options for non-hires 15" models:

http://www.everymac.com/systems/apple/powerbook_g4/specs/powerbook_g4_1.67_15.html
http://www.everymac.com/systems/apple/powerbook_g4/specs/powerbook_g4_1.5_15_2.html

We discussed the latter one 2 years ago there:
https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=7791&forum=11&start=13 :-)

Andreas would (no doubt) be correct on this.
Its never been an issue with me as I don't have an external display that would be legible at these resolutions.

Possibly when I move to a G5/9800 combo I'll look into upgrading my monitor.

I should feel bad since I only care to run 1440x900.