Tiina20 if your fondant is really hard it is O.K. to soften it in the microwave. I have done it on many occasions. Just be very careful as it melts from the centre first. Put it in for 10-15 seconds at the most the first time, give it a knead and then put it back in for 10 second or less bursts, with a bit of a knead in between. I have never had to put it in for more than about 25 seconds. It will still need to be kneaded properly before you roll it out but you won't be exhausted from all the kneading. If it ends up a bit soft then you will need to wait until it cools down before using. Nowadays I am using Satin Ice. It is a lot softer than some brands and I find that I never have to microwave it before kneading.
Hey cazza1, thanks for your reply, good to know as most of the times i end up with some fondant on the plate :P its true it does melt center first