Can i change my front fork on my fixed gear so i dont have to use a 21.1mm quill stem?

i want to change my fork so i can use a threadless setup but im not sure what will fit in the head tube since right now i can only use a 21.1 mm quill stem. im mainly wondering if the inside diameter of my fork effects how big my head tube is.Can i change my front fork on my fixed gear so i dont have to use a 21.1mm quill stem?
You could change your fork, but you'd need a new headset too, and that's probably more money than you want to spend. Get a stem adapter:

http://www.performancebike.com/bikes//Ca



Replace your quill stem with this and them you can use any threadless stem you want. You'll need the one inch size which will adapt to a 1 1/8 threadless stem.