If you have Maya 6 -- you can generate normal maps then switch those normal maps to displacement (which can be used as bump) maps using:
How to use Maya's TransferSurface plugin to create the normal map is something someone else will need to explain. Never did it yet and I don't want to copy verbatem from a book.
The basic gyst is: You duplicate your model and add a shit load of detail to it in geometry. Then you overlap them and say "Maya, give me a map to make the low-poly one look like the high poly one" And then Maya says "Fine but you better not be playing games in the background, I need your CPU's loving" and then you say "Oh quiet Maya, I saw you kissing up to the Videocard last night... swapping with its GRAM." And then Maya blushes and does your job.