ATI Radeon X1900 XT PowerPC G5 Leopard Issues

I have a Power Mac G5 2Ghz (not a Mac Pro) with an ATI Radeon X1900 XT in addition to the original NVIDIA GeForce 6600LE graphics card. All was wonderful, until I installed Leopard. Then any monitor connected to the ATI was showing thin blue horizontal lines and the machine locked up the screen saver kicked in. It would also lock up when dragging an application to or from the ATI connected monitor. I opened tickets with both AMI and Apple, and they both point fingers at each other. I've cleaned the card several times and the latest AMI drivers have been installed, to no avail.

I do not want to back off of Leopard if at all possible. Has anyone experienced these issues and if so is there a resolution?

Thanks,
Vfalzone

my machine specs below:
Model Name: Power Mac G5
Model Identifier: PowerMac11,2
Processor Name: PowerPC G5 (1.0)
Processor Speed: 2 GHz
Number Of CPUs: 2
L2 Cache (per CPU): 1 MB
Memory: 2 GB
Bus Speed: 1 GHz
Boot ROM Version: 5.2.7f1

ATI Radeon X1900 XT:

Chipset Model: ATY,RadeonX1900
Type: Display
Bus: PCIe
Slot: SLOT-1
PCIe Lane Width: x16
VRAM (Total): 256 MB
Vendor: ATI (0x1002)
Device ID: 0x7240
Revision ID: 0x0000
ROM Revision: 113-A52070-109

When owned a Dual Core G5 had this problem. Is the card a flashed PC card or the Radeon X1900GT? The flashed card caused precisely the problems you describe whereas a specific Mac card did not.