PCI memory overflow on AGP

One of my colleagues has reported a bug with our GL application on a NVIDIA PCI card running under windows 2000 on a pentiumIII PC with AGP. He is using the PCi card and gets a severe crash requireing reboot, after trying to load textures into memory using Glbindtexture and gltextimage2d. Sometimes he gets a error code back which when interrpreted signals a directX surface out video memory error??? GL uses DirectX surface??. I dont have any PCi cards so I cant test this problem. With an AGP card we see no problems. I have no experience with PCI cards, any suggestions??
We typically load up to 200MB of textures, which can range from 256sq to 1024 sq. Our application shows items in stores and therefore depending on the user viewpoint lots of diffeent textures can be needed.
Is this simply that the card (16mb mem) can only hold a finite sum of texture’s while AGP uses a larger memory pool. Does PCI not also use system memory??