PowerMac G4 Quicksilver 1.8GHz.
Started at 1.4GB free.
Runs at 0.4GB free.

Radeon9000 128MB
61MB used after closing all other windows (except Ambient and 1 Ambient Panel while running 1600x1024 in 24bit

Hint:
Set Ambient to lowres screen, close all windows and it should be just enough.