Aha!! IT WORKS! I'm using it now!
Here's what I did THIS time.
1) CLEAN INSTALLATION OF WINDOWS. Used nLite
to strip unnecessary "features" prior to installation. Left Windows' Wireless Zero Configuration service, as I'm sure several nonstandard drivers rely on it.
2) Installed the drivers for ALL the system components - but NOT the craplet software. This includes the Intel chipset software from Intel.com (NOT gateway), for the i855PM chipset, the ATI driver from Gateway, the modem driver from Gateway, and the sound driver from Gateway.
3) Installed the driver from gigabyte-usa.com (good luck navigating the site
4) Was left with the Hardware Disabled message, read through this thread, and tried using a CMOS-clearing utility. This wiped the BIOS but the wireless is still disabled. I don't know how the hell they pulled that off - apparently another onboard chip contains the wireless on/off state that's being backed by the battery. The CMOS-clearing may just be a result of clearing this other chip.
5) Took the whole damn thing apart, pulled the battery plug off. Remembered shortly after that I should remove the main battery as well. Started toying around with parts a bit, pulled out the wireless card, plugged it back in, took off the CPU cooler (I'm bored here!), tried to see if I could pull out the CPU just for curiosity's sake, failed, reassembled the cooler, started putting the plate back on, realized the battery was unplugged, plugged the CMOS battery back in, put the system back together, plugged the main battery back in.
6) Started up on battery power (like many of these steps, probably not necessary but I'm going over EVERYTHING I did), entered BIOS setup and reset the date and time to the right settings. Also changed some other settings to my preference (screen stretch disabled, boot order HDD first, diagnostic screen enabled, etc), and let Windows boot. Logged in and voila, no more "no"-sign covering the icon!
And, it now works. I will never let wbutton.exe touch my computer. Ever. Ever, ever.
As for your direct problem, it's probably just an antenna problem. :-)
Hope this helps at least someone!
edit: If it asked for the time and date, it was reset. A BIOS update can never be reverted, as it's stored in flash. Don't expect your old BIOS version date to come back after resetting. All the settings will be restored to default though (notably, you'll get the big Gateway screen instead of the text display if you had it set like that). Also, I left mine unplugged for about 6 minutes.