Johan over at MVKTech sends word of the latest update to their NiBiTer GeForce BIOS Editing tool. Here is the change log.
Added support for:
GeForce 6200 TC PCI-E
GeForce 6600 PCI-E
GeForce 6600 GT PCI-E
GeForce FX5300 PCI-E
GeForce FX5900 ZT
Quadro FX540 PCI-E
Fixed Gainward 6800GT GS memory speed
Fixed Gainward 6800U speeds reversed
Added Adv. Info tab to edit various IDs manually
Added Boot Settings tab with option to edit bootup text, bootup display settings, fastwrites/sideband addressing
General info shows additional BIOS date and product info

Added integrity indicator for quick checking BIOS files
BIOS version now read from internal version, not bootup string
Added support for GeForce 6xxx timings
Redone GeForce FX5xxx timings
Added support for new GeForce 6600GTs voltage table
Added support for enabling GeForce 6600 temp monitor trick
Device naming synced with ForceWare drivers
Various bugfixes and improvements

http://www.mvktech.net/content/view/1176