Installation

You don't need to flash another BIOS.

Download the latest version of "Softmodded Display Driver" from the downloads page.
Run it.
Follow the instructions on screen (ATI Display Drivers Setup should start after extraction).
If you are prompted about a component that did not pass the Windows Logo Test, continue the installation. Windows just notified you that you are installing a patched file :)
Finish
Download and install "Control Panel" if you haven't done so yet.
If you have an All-In-Wonder card, download and install the "WDM Capture Driver".

OR (if you already have the driver package and just want to download the patched driver file)

Run the driver installer and update your display drivers. Verify that the (still unmodified) driver works at this point.
Download the version of "Patched ati2mtag.sys" from the downloads page which matches the driver version you want to install.
Extract the "Patched ati2mtag.sys" zip file you just downloaded into an existing folder with a name similar to "2KXP_INF\B_xxxx" where the driver installer extracted the files to.
Delete the "ati2mtag.sy_" file there.
In Device Manager right-click on "Radeon 9700/9500 SERIES" or "All-In-Wonder 9800 Series"...
Update Driver...
Install from a list... (2nd option)
Don't search. I will choose the driver... (4th option)
Click "Have Disk" and navigate to the "2KXP_INF" driver directory...
Select the appropriate driver. If you have duplicate entries- choose any it does not matter.
Click "Finish", then reboot
Use ATITool to check the number of active pipelines (settings -> overclocking).