There was quite a long thread about this problem a few months ago.
One suggestion that I remember reading was to make vertical saw-cuts in the back of the skirting every few inches (more or less, depending on how tight the curve is). There was something else about soaking the wood first and then cramping it into the desired curve, but no doubt others with better memories will be more precise.
Yep - mark up the back with your square. the closeness of the saw cuts will determine how tight a radius you can achieve. Also the depth of the cuts. Get another length or two of board of the same dimentions and play around till you get it right. Be prepared to make a lot of cock ups before you get the measure of it. Mike.
I agree with Mike. Loads of vertical sawcuts in the back is the way to go.
The soaking/steaming and bending technique is very specialised and requires a considerable amount of specialist equipment.