OP stands for "Original Poster". I.e. the person who started this thread. I.e. you.
I get very similar results to you when I try to modprobe agpgart (the 'no such device', etc.). I'm also running (possibly not for much longer) redhat 9. I had no problem applying the patches in the nvidia driver distribution to my kernel. At least, 'patch' did not come up with any errors. I compiled a custom kernel with /dev/agpgart support disabled (not even a module), and used 'Option "NvAGP" "1"' in XF86Config.
As far as I can see, AGP itself is running. At least, XFree86Config.0.log reports that option "1" has been requested, and my agp status is listed as enabled.
Life would be perfect if it wasn't for thisone small glitch....