Collision with diagonal surface

Ok, I'm having a bit of a problem with this.

A ball is dropping in free fall (not spinning/rotating or anything).
After a given time it collides with a diagonal surface (a total inelastic collision), it then begins to roll down from it.

How do I find the velocity that it begins to roll down the diagonal surface with? Do I just regard the ball's velocity as a vector and find the component that is parallel to the surface?

>>10 has the a pretty good answer, but it looks like he assumes that the impulse upon landing is perfectly perpendicular to the plane (ie no frictional impulse) this corresponds to 0 deformation of either the ball or the slope during the collision, this, of course, means no energy loss (aka perfectly elastic collision)  This also means that the ball picks up no rotational velocity in the collision and the ball begins by skidding down the slope.
But we specified an INelastic collision so let's consider the more likely scenario that the collision's frictional factor is enough that the ball doesn't skid at all.
r=radius
m=mass
I=moment of inertia
F=impulse due to friction
t=torque=F*r
w=final rotational velocity=t/I=v/(2*pi*r)
v0=speed before collision
v=final speed=v0*sin(theta)-F/m
This gives:  2*pi*F*r^2/I=v0*sin(theta)-F/m
F=v0*sin(theta)/(2*pi*r^2/I+1/m)
So our actual starting velocity is: v=v0*sin(theta)*(1-1/(1+2*pi*r^2*m/I))
If the ball is uniform then I=2*m*r^2/5 and v simplifies to:
v=v0*sin(theta)*(1-1/(1+5*pi))=v0*sin(theta)*(5*pi/(1+5*pi))
In practice you would have a slightly smaller value for v since r temporarily shrinks when the ball collides.