On a 500Mhz --> acceptable speed
(probably loooooong render times)
on a 333Mhz --> 2/3 acceptable speed
(probably looooooooong render times)
On a 1.7GHz P4 --> great speed :)

Throw in more memory too. 128Mb is too little to enjoy even Poser4. Think 512Mb or more.

Better upgrade to a faster system. If you are on a 333Mhz, other components in your computer will be too slow as well, like e.g. memory to CPU bus speed etc.