SpeedFan should work on old hardware like yours. The problems show up on new hardware because development for the program stopped a while ago.
It's normal that you didn't find out how SpeedFan works. It's really weird to use and no one understands it by themselves.
First thing to know is, SpeedFan will by default not control the fan headers of your board. You first have to unlock the board's PWM controls. You do this on the "Advanced" tab in SpeedFan.
In that Advanced tab, you select the board's sensor chip in the pull-down menu box at the top. Then next, you'll see entries listed with the word "PWM" in the name. Those PWM entries are the fan headers of the board. You select one of those entries, and then you switch it to "manual". Then look at the bottom right of the window and click on the "remember" check-box. This "remember" check box is important.
After you have done this, you will be able to play around with manually setting your fan speeds in the main window of the program. You have to close the settings window to be able to click on stuff in the program's main window. Things to do there is to just play around with the + and - buttons to learn which of the controls are what fan header on your board, and learn how your fans react.
Then next, about how to do your automatic fan setup, you have to know that the control settings on the "temperature", "fans" and "speeds" tabs are not what you'll want to use. The settings on those tabs will get (mostly) ignored after you have set up a fan curve on the "fan control" tab. But on those tabs there's still the alarm/max temperatures that are important. If those max temperatures are reached, the fans will go to full speed and will override your curve from the "fan control" tab. This means you'll want to set max temperatures to something you'll never reach normally so that it doesn't interfere with your curves.
Then last thing, you create your setup on the "fan control" tab. You can select inputs there and draw your curves. What's interesting to know here is, you can have multiple inputs that combine to the same speed output. That's interesting because you can make it so both the CPU and the GPU temperature can increase your case fan speeds. There's a "method" box on the right side that you'll want to change to "max of speeds" for this, it's by default set to "sum of speeds".
Thank you! Playing around in the advanced tab, I was able to manually control the CPU Fan! The directions aren't that clear...
This is great, and will greatly extend the reliability of this old rig..