How to make a fan speed regulator with a pot and a voltage regulator?
You can try this. It might not be the best but it uses the parts you have. 

Range is a bit less than 6V to about 9.5V so you can't set it to full speed. 

The 6V low end is more of a feature since most computer fans will stall if you drop the voltage too low. 







simulate this circuit &ndash; Schematic created using CircuitLab

Pretty much any PNP transistor can be used for Q1 (well, don't use a 4GHz RF part).