You are talking way over my head now! Sorry. I have only been playing with Linux for a year and I have no formal computer training. I'm learning as I go along.
My system is an HP Pavilion 750N which uses an ASUS P4B266-LA motherboard. It uses the Intel 82845 845 (Brokedale) rev 04 PCI/AGPchipset. In the BIOS there is this option "Default Primary Video Adapter - PCI or AGP" When I first bought the system it used a RIVA TNT2 and was set to 'PCI' but when I plugged in the FX5200 card, I reset it to 'AGP'. I didn't know why it was set to 'PCI' in the first place (I still don't!) but it just seemed logical to set it to 'AGP' for the FX5200. Everything worked well so I forgot about it, until today. I reset it back to 'PCI'. Still cannot start X in Debian but all still works in Red Hat.
As for the APGART and NVAGP, I know nothing about either except that they are modules and that I'm using APGART here in Red Hat (lsmod). NVAGP I never heard off so, please, fill me in. How would I invoke NVAGP? And I'm sure I would need to remove AGPART first. I think I know the commands but, again, any and all help is appreciated!
BTW, what's the difference between APGART and NVAGP?