Prob upgrading Dell 8300 with BFG 6800 Ultra OC

I am unable to install the 6800 Ultra OC AGP on my Dell 8300 - can anyone provide any assistance? I just spent an hour on the phone with Dell tech support and believe the system is set up correctly to accept the card.

System:
Dell 8300 with upgraded A07 bios
(upgraded PSU from 305 to 410w)
GeForce 5200 AGP 8x 128 meg RAM
NVIDIA 84.21 drivers
Windows XP Home

I have gone through the Quick Install guide, removed the drivers, prior to installing the 6800. Going through the BIOS, the only settings that could be changed were AGP aperture (changed it to 256)

There are two apparent errors, the first occurs prior to loading Windows drivers:

ERROR 1:
On boot, I get horizontal lines across the screen (prior to Windows drivers loading) as shown here: Pic #1
Once Windows starts loading I get similar corruption: Pic #2

ERROR 2:
Even though the existing video card uses NVIDIA drivers, I followed the instructions to remove the drivers using the control panel prior to rebooting and installing the 6800. Then, when I try to install the video card drivers (NVIDIA 82.41), I get the blue screen of death which calls out these errors:

PAGE_FAULT_IN_NONPAGED_AREA
nv4_mini.sys

I've done a lot of googling around, you can find the error message, many times its BIOS related but apparently my BIOS is set up correctly, I already have a GeForce AGP card working fine.

I did try to call the 24x7 BFG tech support but have not been able to get through despite hold times of 15,30, and 55+ minutes. They suck! I did send email this evening.

Any suggestions?

TP: I understand the requirements. I've got a good PSU (http://www.pcpowercooling.com/produc...php?show=S41D2) that peaks at 450w and the system doesn't draw much (single hard drive/optical drive/no PCI boards).

Good suggestion on the drivers, however, note that on boot I'm getting video conflicts/corruption - that's before windows drivers can even load.

TP: Both very good suggestions that I'll follow. Thanks!