Frustum planes

Can anybody ask to me how can I get frustum planes from projection matrix
like at
For me interesting mathematical side of this question.

You can use gluUnProject to get those eight corners of the frustum. From the corners’ coordinates, you can get the equation of each planes.
About the mathematics behind, it’s the inverse of the product of Projection matrix and ModelView matrix.

[This message has been edited by Coconut (edited 07-31-2001).]

theres also an example in the faq
with a bit of an explanation