Export to MAP and use BSP Modelers (QUARK, Hammer, GTK) that allow you to import map
Alternatives: No, hidden surface removal is not possible for free geometry at least not in a regular human lifetime. Progressive mesh reduction can be done through the mesh reducer you can buy at www.thegamecreators.com for example.
And "without altering the shape of the mesh" you won't get anything, at least unless the model was done badly upfront with lots of unneeded geometry. (for normal maps etc you don't need real geometry, subdivision modifiers do it as well)
Alternatives: No, hidden surface removal is not possible for free geometry at least not in a regular human lifetime. Progressive mesh reduction can be done through the mesh reducer you can buy at www.thegamecreators.com for example.
And "without altering the shape of the mesh" you won't get anything, at least unless the model was done badly upfront with lots of unneeded geometry. (for normal maps etc you don't need real geometry, subdivision modifiers do it as well)