Integration by parts help.

So I have this integral, intgrl of arctan4xdx, and I can start it off but I get stuck about half way through.
u=arctan4x dv=1dx
du= 1/(1-4x^2) v= x
= xarctan4x - intgrl x/(1-4^2) dx
Now what?

You've made an error in your calculations. du is actually 1 / (1 + 16x^2) if u is arctan(4x). After you've made that correction, you simply need to evaluate the new integral. That can be done using substitution. Let u = 1 + 16x^2 then du = 32x. The rest is straightforward.

Well, let me correct all the mistakes before I help with the integration part.
u = arctan(4x)
du = 4 dx / (1 + (4x)²) = 4 dx / (1 + 16x²)

dv = dx
v = x


Remember that
d/du [arctan(u)] = (du/dx) / (1 + u²)

With that
xarctan(4x) - ∫ 4x dx / (1 + 16x²)

All you need for that integral is simple u-sub (or t-sub since we've already used u and v).
t = 1 + 16x²