more transparency questions

how would i make a plane that is transparent, yet if if part of an object goes behind it, the part thats blocked by it will disappear?
am i making sense? :confused: i’ll try to post sime pictures of what i mean.
thanks

heres what i mean: theres a plane in front of a cube, the plane is supposed to be transparent but isnt here for illustrative purposes:
http://i30.tinypic.com/359hbvq.jpg

here is a mockup i made of what i want (sort of):
http://i27.tinypic.com/1i0l1s.jpg
as you can see, the area where the plane obscured is as if there is nothing there, except for the light gray area on the left, which should also be transparent. i messed up some where in the mockup, but i hope u get the point.
any way to do this?

Hi,

Give the plane a material that has alpha 1.0, and ENV selected.

rawpigeon: thanx, this is exactly what i needed!