my ati radeon 9600 not recognized correctly 1024x768 is ok but refresh rate is not 85hz, how can i solve this isue? mac osx ver. ideneb 10.5.8

Here is my specs:
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ga8ipe-1000 rev 1.0
Processor Name: Intel® Celeron® CPU
Processor Speed: 2 GHz
Memory: 1 GB
Type: Display
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 256 MB
Vendor: ATI (0x1002)
Device ID: 0x4150
Revision ID: 0x0000
Displays:
SwitchResX4 - q770:
Resolution: 1024 x 768
Depth: 32-Bit Color
Core Image: Software
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Not Supported
QuartzGL: Supported

Why would you use an AGP card? You can buy a nice 8500Gt for $20 on ebay http://compare.ebay.com/like/3602901...=263602_263632

Plus its not supported

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OS: Retail Snow Leopard 10.6.5 (Vanilla Install)
Kernel: 10.6.4 Legacy Kernel
Mobo: GA-MA74GM-S2
CPU: AMD II X4 Athlon 630 3.6 GHz
RAM: 4GB GSKILL 800Mhz DDR2
GPU: ASUS 8500GT 512 MB (Quartz Extreme)
Cooling: Corsair H50 Watercooling