Xorg comes up with DRI disabled. The relevant section from Xorg.log seems to be:

(II) intel(0): I830CheckAvailableMemory: 434172 kB available
drmOpenDevice: node name is /dev/dri/card0
drmOpenDevice: open result is -1, (No such device or address)
drmOpenDevice: open result is -1, (No such device or address)
drmOpenDevice: Open failed
drmOpenDevice: node name is /dev/dri/card0
drmOpenDevice: open result is -1, (No such device or address)
drmOpenDevice: open result is -1, (No such device or address)
drmOpenDevice: Open failed
drmOpenByBusid: Searching for BusID pci:0000:00:02.0
drmOpenDevice: node name is /dev/dri/card0
drmOpenDevice: open result is 7, (OK)
drmOpenByBusid: drmOpenMinor returns 7
drmOpenByBusid: drmGetBusid reports pci:0000:00:02.0
(II) [drm] loaded kernel module for "i915" driver.
(II) [drm] DRM interface version 1.3
(II) [drm] DRM open master succeeded.
(II) intel(0): [drm] Using the DRM lock SAREA also for drawables.
(II) intel(0): [drm] framebuffer mapped by ddx driver
(II) intel(0): [drm] added 1 reserved context for kernel
(II) intel(0): X context handle = 0x1
(II) intel(0): [drm] installed DRM signal handler
(==) intel(0): VideoRam: 131072 KB
(**) intel(0): Framebuffer compression disabled
(**) intel(0): Tiling enabled
(II) intel(0): Attempting memory allocation with tiled buffers.
(WW) intel(0): Failed to allocate texture space.
(II) intel(0): Attempting memory allocation with untiled buffers.
(WW) intel(0): Failed to allocate texture space.
(WW) intel(0): Not enough video memory.  Disabling DRI.

I have tried AGP apertures of 64, 128 and 256M in the BIOS with the same results. The system has 512M RAM. The driver ignores the VideoRam option and I have not found another way of hard-wiring the amount of video memory. DRI used to work on the i810 driver.

FWIW, here's the output of lspci:

00:00.0 Host bridge: Intel Corporation 82865G/PE/P DRAM Controller/Host-Hub Interface (rev 02)
00:02.0 VGA compatible controller: Intel Corporation 82865G Integrated Graphics Controller (rev 02)
00:1d.0 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI Controller #1 (rev 02)
00:1d.1 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI Controller #2 (rev 02)
00:1d.2 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI Controller #3 (rev 02)
00:1d.3 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB UHCI Controller #4 (rev 02)
00:1d.7 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB2 EHCI Controller (rev 02)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev c2)
00:1f.0 ISA bridge: Intel Corporation 82801EB/ER (ICH5/ICH5R) LPC Interface Bridge (rev 02)
00:1f.1 IDE interface: Intel Corporation 82801EB/ER (ICH5/ICH5R) IDE Controller (rev 02)
00:1f.3 SMBus: Intel Corporation 82801EB/ER (ICH5/ICH5R) SMBus Controller (rev 02)
00:1f.5 Multimedia audio controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) AC'97 Audio Controller (rev 02)
01:06.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10)
01:07.0 Ethernet controller: 3Com Corporation 3c905B 100BaseTX [Cyclone] (rev 30)
01:08.0 FireWire (IEEE 1394): VIA Technologies, Inc. IEEE 1394 Host Controller (rev 80)

If any other info is required, I'll be happy to follow up with them.