Finding the components of this vector

[opticaltempest]

How is the vector g turning into the scalar g? What am I missing that is
allowing us to represent g as a scalar quantity and no longer a vector
quantity? When going through the algebra to find mg_x, (component
of gravity in the x-direction) I don't see how it turns into a
scalar of 9.8.

http://img124.imageshack.us/img124/3417/page00023ue.jpg

 

[dicerandom]

When they say $g$ instead of $\vec{g}$ they mean the magnitude of $\vec{g}$, i.e. $g=|\vec{g}| = \sqrt{g_x^2 + g_y^2}$.