the only problem I see is that most macmini's had 32mb vram, and only the last models had 64mb vram, which is not enough.
I know my efika at 1680x1050 with 128mb vram on a radeon agp card has some shearing/tearing... I dont even know if 1680x1050 would even work on 64mb ram let alone 32mb vram...
The mini's were close in design to some of the older powermacs so that might be a better option to get one of the mirror door, etc models that you can replace the gfx card...
