My suggestion is a Powerbook 1.67 GHz with 1.5 GB RAM.
It's a pretty nice maschine: well supported, small, silent, mobile, energy efficient, rather slick looking (depends on how careful the previous owner was, my Powerbook looks as good as if it came straight ot of the box) and pretty fast.
The non support of the R300 for W3D is the only downer i am aware of, but there's not much W3D stuff which cannot be replaced. For example the already mentioned WO2097 is said to run even better in FPSE emulator than the WarpOS version.