How can I change fan speeds on my PC?

I'm trying to use SpeedFan but I don't know what to configure because I don't know the model and type of motherboard I have.

I have an Intel Pentium 4 CPU with HT enabled and 3.20 GHz clock speed. Bus speed is 200 MHz and rated FSB 800 MHz.

I used CPU-Z and it told me I had an Intel D915GRO motherboard but I can't find Intel in speedfan.How can I change fan speeds on my PC?
You might want to consider something like this:

http://www.coolermaster.com/index.php?LTHow can I change fan speeds on my PC?
which fan r u talking abt

CPU or case fan

if a case fan u might no be able to change the speed

but if ur talking abt CPU fan let me tell u that CPU fan speed is controlled according to load on it

so as ur CPU gets busier then ur fan gets proportionally faster

nd tweaking the fan speed might result in the improper heat flow so do it wiselyHow can I change fan speeds on my PC?
In speedfan, there is a option called fan speed. Its in %. Increase it.How can I change fan speeds on my PC?
No it was constant you can't change it....try replace new one if it makes more sound