Problem with Stencil Buffer and Radeon 9700 pro

My little app is using stencil buffer to do shadow(based on NEHE tut),everything is ok on my comp(Celeron 600 GeForce 2 GTS and 320 MRam) but on my bro’s new comp(Athlon 2400+,Radeon 9700 Pro and 512 MRams DDR)the shadow doesnt appear???Any hint on what could be the cause???Everything else is ok,only the shadow(he got the last catalyst drivers)…

Thank for any help you could share.

I think that I read a long time ago something about ATI and that demo on the NeHe page. Have you downloaded the current version?