And you're the "Mac expert" in the shop?
...
In that case, anything slower than a quad Mac Pro tower is useless }
Well, to be serious, I second the above - G3/500 G4/400 with >192MB of RAM (>300MB is better) and OS X. You can probably make up the RAM from trashed machines. This is from personal experience comparing my Beige G4 with my dad's PIII-800.
But also to be serious - most of the CPUs you'll be seeing could be called "upgrades", couldn't they? They're almost all socketed. Just pull and keep every single one
Better than they all go to the compactor. Same goes for PCI and AGP cards (as they "won't work in a PC" } ), Comm Slot cards, AV cards, etc.You could have quite a sweet little side business in Mac CPUs and accessories.