sudo nano /System/Library/Extensions/ATIRadeonX1000.kext/Contents/Info.plist
line: <key>IOPCIMatch</key>
add or replace 0x71001002 (double check with command lspci -nnvv. same card here but you pasted a different vend ID)
in com.apple.boot.plist add:
<key>Graphics Mode</key>
<string>1280x1024x32</string>
This works ok for me (in Snow Leopard): you get the resolution and acceleration, no calibration and it looks more like thousands instead of Millions of colors.
Looking for a better solutions my self.
QUOTE (Diabloproductions @ Oct 20 2009, 01:25 PM)

I am looking for a link for a working kext (diaboliks maybe?) for the x1800 under 10.5.8
Has anyone had full functionality with the x1800 under 10.5.8?
Dual monitor DVI working?
etc etc
Card: ATI Sapphire x1800
Device ID: 1002 7109