Take another look at what the latest BIOS fixes..."Patch old K7 CPU without thermal diode can not install XP"
Your Athlon 1000 is an "old K7 CPU" which apparently does not have a thermal diode. That would explain the false temp reading of 99C. (I'm guessing that this temp reading somehow prevents WinXP from installing). AMD rates your CPU's "max die temp" at 90C..if it was actually 99C, the CPU would cease to function. I should have recommended that you try the "touch method". At 99C your heatsink would have been "VERY HOT" to the touch! But I'm sure if you would have carefully touched it, you would have found that it was warm but not "VERY HOT"...it's a crude method, but it would have given you a general idea of the temp.
As for the BIOS flash...there are a few different methods of doing it. Personally, I prefer the DOS method of flashing & that's the method I'm going to explain:
Start by downloading the necessary BIOS & flash utility files from the ECS website:
http://www.ecsusa.com/downloads/downloads_main.cfm?to=Motherboard
Both files are in zip format & will have to be unzipped 1st.
1. copy the new BIOS (7GM831.BIN) & DOS flash utility (AWD860I.EXE) to a freshly formatted floppy
2. if you don't already have a WinME boot floppy, go to bootdisk.com & download the file to create one (get the OEM version)
http://www.bootdisk.com/bootdisk.htm
3. check your BIOS settings...make sure the floppy is set as the 1st boot device
4. boot off the WinME boot floppy that you just created & choose option #4 - Minimal Boot. When it stops at the A:\> prompt, remove the boot floppy & insert the floppy with the BIOS files
5. at the A:\> prompt, type AWD860I & hit ENTER...like so
A:\>AWD860I [enter]
That will start the flash utility. From there, you just have to follow the instructions.
File to Program: 7GM831.BIN
Do You Want To Save BIOS? Y
Save BIOS As: OLDBIOS.BIN
Are You Sure To Program? Y
Then just wait for a message that says, Flashing Complete, Remove Disk & Hit F1.
When it reboots, go directly into the BIOS & double check all the settings...some may have changed, or you may even find that there are some new choices. Correct them as necessary, then try to install WinXP.
ASUS A7N8X-X
Athlon XP 1800+
8.5 x 200MHz
1024MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB
WinME/WinXP Pro SP2