Old 00' Gateway needs Video card to work

[rivrbyte]

Ok...everytime I (TRY TO) help my friends with their computers sometimes things happen. The same friend we have been talking about with the video/sound card issues....It's a Gateway from his work,which they gave away a few years back. ( Manufactured in 7/2000) Pentium III / 200 WATT PSU / 256 SDRAM / 550 MHz / 100 Frint side bus / AGP Nvidia TNT2 Riva 64 / Windows98...(they did give him a Startup disc or a OS CD with it,so we are bassically using the same Operating System,with no support, that should have came with it). Anyway, he called me up to tell me that he was only seeing 16 colors 640x480. I tried to download that Nividia Unified driver which I copied to the his hard drive,but a Error message came up that it could not install because it can not find the nivida chip to make that device work.
I went to gateway chat to talk with a online tech, he told me the AGP is 1x and today's software does not support it,so I would need to buy a Jaton GF FX 5200 PCI card for 85.00!!! he said that would be the only card this system can use. I almost bought a Diamond 7000 128,but he said that would not have worked....OR just buy a new computer. Well, they are not gamers,just want to use their AOL which needs 256 colors to operate.I know they paid nothing for this puter,but he is having a Hip replaced and 5500.00 dental work,so Money is hard to spend for a new computer.
If there are not any cards out there to use with this system, (at a low price) this is a Gateway,is there any reason why I (if he came into some money) just to replace the motherboard and start over again,since we already have the keyboard,mouse, printer,and monitor? I would like to know.

Before I called Gateway, I did everything imaginable you guys told me to do,remove Graphics adapter in Device Mgr,shut down, remove card,reboot, shut down,and reinstall card and tried to install driver....This system does not have onboard video,so I could not see anything on the Monitor while the card was out) I also got a yellow exclamation mark next to PCI MULTIMEDIA device.

On the sound, speakers are on, connected,nut there is no volume control on task bar,I went into Accesories> Entertainment> Volume control, and it doesn't look enabled. Also went to Windows SET UP and in MULTIMEDIA the volume is checked on. Is it possible,it is in the wrong IRQ?

Thank you once again for all your help. And if buying a new MoBo is an option, can this work? I'll have to buy more memory, of course,but Can I use my old Pentium 4 celeron 2.0 s478 on this board?
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ECS 648FX-A SiS 648FX Motherboard

Intel Solution Motherboard - Socket 478:
Outpost #: 3798456
Chipset: SiS 648FX
Processor Support: Intel Pentium 4 upto 3.0GHz ( 533/800 FSB)
Memory Support: Up to 2GB PC 3200 DDR DRAM
Expansion Slot: 1x (8X) AGP, 5x PCI,
Other Features: 6.Ch Audio, USB 2.0 .....................On sale 30.00!!!
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My 478 Cel 2.0 uses 266/PC2100 DDR memory,,,would this above board use the cel 2.o regardless of what memory it uses? (ie: 533/800 ) or too slow for CPU?