Here's what you do.
1) Go
here and download an ISO image of the Ultimate Boot CD.
2) Burn all the applicable files needed for flashing on a CD-RW (recommended, I went through 4 discs before I had all the files I needed). At a bare minimum, I'd have the original BIOS obtained from a dump using ATI Tray Tools, an XT PE BIOS with the core/mem speeds set to default Pro speeds, and finally ATIFlash.
3) Boot up with the UBCD. After booting, hit "F1" for "Mainboard Tools", right-arrow twice to bring you to BIOS Utilities, then "F1" again for the first BIOS utility.
4) After the BIOS utility starts loading, hit "OK" each prompt to accept defaults (these should be fine for most systems). You'll be at a command prompt that looks something like:
T:\dos\apps>
5) Do a: "cd t:\" (without quotes) to bring you to the root dir of the disc, then pop your BIOS disc in.
6) Run your flasher. Typical usage would be:
Step 1:
atiflash -f -p 0 xtpe.bin -newbios
(substitute "xtpe.bin" for whatever you named the 16-pipe BIOS you'll be using)
Step 2: (without rebooting)
atiflash -f -p 0 oldbios.bin
(no "newbios" switch, oldbios.bin being the backup you made with ATI Tray Tools)
6) Reboot into Windows and use ATI Tray Tools or ATI Tool to check if your pipes are unlocked.
Good luck!