|Speedfan, or any other utility can only alter the speed of any fans if there is a suitable sensor inbuilt in the motherboard together with the necessary controller circuit/chip|
The documentation I've seen so far on that vintage machine shows only passive cooling for the CPU so what fan are you referring to? If there is a CPU fan in your tower then it may have been fitted after-market. Or there might be a case-fan and of course there will be a powersupply fan. None of these will be controllable unless they are wired through a separate controller. What is the real issue you have that leads you to ask about controlling the fan speeds in this machine?
Goin' Fishin' (Some day)