The i810 driver is a bit different from the others in that it 
absolutely requires agp, and a different version from what the other 
driver use. This is partly historical: the chipset requires features 
that weren't available in the 2.2 driver when it was first rewritten, 
and no one's gotten around to porting to the new one since. It uses 
it's own copy of the agpgart.h header.

There's also a patch available that might fix this. see 
http://lists.sourceforge.net/pipermail/utah-glx-dev/2000-March/001548.html

Here's what Keith Whitwell had to say in a recent message to the list:

For now you need to use

        - the XFCom server
        - the I810Gtt gart (oldgart) that comes with the server
        - current GLX 

The current GLX code is quite a bit slower than it needs to be (on the 
order of 50% slower) because I haven't implemented tiled memory on Utah.

http://lists.sourceforge.net/pipermail/utah-glx-users/2000-March/000513.html