hi velarde,

like max suggested, running carrara with only the extensions you absolutely need is a good way to get more speed out of your computer.

my question for you is, does the slow down you speak of pertain to the rendering time, or the fluidness of the interactive render? (the Gouraud live preview)

if the slow down is in the interactive render, then my guess is that it is the number of objects (polygons) in proportion to your ram and processor speed.

however, if the slow down is in just the render, there are many things you can do.

i would recommend buying "digital lighting and rendering" by jeremy birn.

it has many tips for speeding up renderings, as well as just achieving a better image. you won't regret the buy.

-scott