I''m just starting to write my culling functions but i can already see a problem waiting to happen. When objects enter or leave trhe frustrum they are going to just pop up or disappear due to the rigid nature of the frustrum shape (like in many older psx games). How can i prevent this? I thought about setting the far plane of the frustum to a very high distance and only clip objects to the sides of it? Is this feasible or will i get a big performance hit?

are you clipping by the center of the object? why not a bounding radius, its fairly easy to test the center of an object with a radius against a plane. take the radius of your sphere, multiply it by the planes normal that you are testing multiplyed by -1. add that to the center of the sphere(what you are probably testing now), and test THAT point against the frustrum. you may have to take out the -1 depending on which way the frustrum planes go.