How do we learn this?I for one have no idea how to do that do-it-yourself flash ROM thing. Where do we learn how to do it and on what cards?
Don't we have to own a PC to do it?
A quick summary:
Flashing a video card to the Mac involves taking the ROM file from an OEM Mac video card and "flashing", or copying, that ROM file to a similar PC video card. Depending on how similar the two cards are the flash may be totally successful, partially successful or a failure. Thus, PC cards that have the most similar board layout to the original Mac card are most likely to work.
Many PC vido cards can be flashed to G4 and G5 Macs. The procedure is different depending on what class of card (and specific type of card within that class) you are flashing as well as what Mac you intend to use it in.
The following PC cards can be flashed to AGP-equipped G5s and certain G4 towers:
GeForce 7800GS,7800GT, 7800GTX (hacked ROM not publicly available)
GeForce 6800, 6800GS, 6800GT, 6800 Ultra
GeForce 7600GS, 7600GT (still a work in progress and not public yet)
GeForce 6200 (hacked ROM not publicly available)
GeForce 5200/5200 Ultra, 5500/5500 Ultra
GeForce 4200ti/4600ti
GeForce 3ti
GeForce 4MX/2MX (why bother these days?

)
Rage 128/Pro Turbo etc (again, why?

)
Radeon 7000/7500
Radeon 8500
Radeon 9000
Radeon 9100
Radeon 9200
Radeon 9500/9500 Pro
Radeon 9700/9700 Pro
Radeon 9800/9800 Pro/9800XT
Radeon X800, X800 Pro, X800GT, X800XT, X800XT Platinum Edition (VGA only)
Radeon X850 Pro, X850XT, X850XT Platinum Edition (VGA only)
FireGL X3 (flashes with X800XT ROM and has dual functioning DVI)
Radeon X1900XT PCIe (for Mac Pro)
Not all of these cards work with all Macs: for instance the GeForce 6800 series does not work reliably on Mirrored Drive Door (MDD) Macs but functions well with Digital Audio, Quicksilver and G5 Macs. Some of the older cards may not work in a G5 (not really an issue).
Depending on which brand and model of card you get, you may have to perform some significant modifications to get the card to work (soldering or changing values in the ROM file).
Some cards however, like the Radeon 9800 Pro, X800XT and GeForce 6800GS/GT/Ultra among others can be flashed with no modifications.
Flashing is sometimes done on a Mac, but sometimes it requires a PC. Some cards can be flashed on either machine.
The
Strangedogs video card flashing forum hosts the hacked ROM files and the forums contain all the information on how to flash the cards. However, the site is difficult to navigate and you have to dig to get what you need. But it's there.
Unfortunately, some of the ROMs are not publicly available. Cards like the 7800 and 6200 series must be purchased already modified from Strangedogs members who have access to the hacked ROM. At the moment they have been inundated with orders and have stopped supplying these cards. Still, many ROMs for powerful cards like the 6800 and X8xx series are available for do-it-yourselfers. Click the link in my signature to read how I flashed a GeForce 6800GT for my G4 tower.