The scaling factors are the sizes of the heterogeneous vectors constituting the top-left 3x3 block. Dividing these vectors so that each is unitary, you're left with a rotation matrix. For (a column-vector) example:

The rotation-scaling-translation matrix:

a11 a12 a13 a14a21 a22 a23 a24a31 a32 a33 a34 0   0   0   1

Translation vector = (a14, a24, a34)

The rotation-scaling matrix:

a11 a12 a13 0a21 a22 a23 0a31 a32 a33 0 0   0   0  1

XScale = sqrt(a11² + a12² + a13²)
YScale = sqrt(a21² + a22² + a23²)
ZScale = sqrt(a31² + a32² + a33²)

The rotation matrix:

a11/XScale a12/XScale a13/XScale 0a21/YScale a22/YScale a23/YScale 0a31/ZScale a32/ZScale a33/ZScale 0    0          0          0      1

Now, calculating the rotation quaternion is a little more involved, so I'll link you to this FAQ.

Admiral