Rendering to depth texture on ATI card

Hi,

I have some code that currently renders to a depth texture using the extension WGL_ARB_pbuffer and WGL_ARB_render_texture. Here is some sample code I am using:

Pbuffer.Activate();
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();

		glMultMatrixd(o_matv);

		glViewport(0,0,TEXSIZE,TEXSIZE);
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();

		glMultMatrixd(matlookv);
		
		glEnable(GL_DEPTH_TEST);
		glDepthFunc(GL_LEQUAL);

		glPolygonOffset(1.4,1);
		glEnable(GL_POLYGON_OFFSET_FILL);

		render_geometry(1);
		glDisable(GL_POLYGON_OFFSET_FILL);
		glBindTexture(GL_TEXTURE_2D,depth);
		glCopyTexSubImage2D(GL_TEXTURE_2D,0,0,0,0,0,TEXSIZE,TEXSIZE);
Pbuffer.Deactivate();  

This code works perfectly on an Nvidia card and I can even use glGetTexImage to verify the depth texture is being created correctly. However, on an ATI card. My program does not work and glGetTexImage returns a blank texture. I’ve also read on other forums that ATI cards do not support direct rendering to depth texture via a pbuffer. Is this true, and if it is, does anyone know a workaround for ATI cards? I’m using a FireGL V3100, by the way, if that matters.