I'm sorry, but WIM32's formula looks a little strange. There should be a pi and no exponents. Also, the initial constant should be close to unity.
For the P201 window I have:
a0=0.999028
a1=2*0.925752
a2=2*0.351960
a3=0
a4=0
w = a0 - a1*cos(2*pi*t/T) + a2*cos(4*pi*t/T) - a3*cos(6*pi*t/T) + a4*cos(8*pi*t/T)
I hope this helps, Troy