Apple had been doing GPU-accelerated GUIs since the early NeXT days; it was certainly possible on hardware weaker than what Vista required.
Windows 3.1, with the aproppiated drivers and modern SVGA card, had accelerated 2d graphics. Accelerated GUIs don't even need GPU or 3d.
I mean Apple had a GPU-accelerated GUI in 1990, but probably not what we think of "GPU accelerated" these days
https://wiki.preterhuman.net/Apple_Macintosh_Display_Card_8-...
Minor correction: Apple introduced GPU-accelerated GUI in 10.2 with the introduction of Quartz Extreme.
Display PostScript did not have GPU acceleration, as far as I know.
https://en.wikipedia.org/wiki/Quartz_Compositor?#Quartz_Extr...