picking

hi! i''m working on a terrain editor and everything worked fine for a while...i''m using the same picking parameters as in NeHe''s tutorial and on my old graphics card ( Riva TNT2 ) it was working OK, but on my new one ( ATI Radeon 7000 ), it works only now and then...does anyone have a clue about what changes do i have to make to my code? picking parameters are as follows: gluPickMatrix((GLdouble) mouse_x, (GLdouble) (viewport[3]-mouse_y), 1.0f, 1.0f, viewport); i''ve read a post, some time ago in which someone complained that on his/her ATI the NeHe shadows tutorial ( No. 28 i think ), didn''t work right, so the explanation was that ATIs have more precise stencil buffer... anyone had similar experience with picking? thanks in advance follow the yellow brick road