Using Immoral means to accomplish moral ends

Is using immoral means to accomplish moral ends justifiable?

Prostitution to feed your kids or pay for school;
Stealing to put food on the table for your family;
Lying in an interview in order to get employed; etc.

Is it wrong? Is there a time when it can be justifiable?

The questions above may lead to even broader questions such as: who defines what is immoral and what is moral? Should we let society judge our actions or should we be driven by our own convictions?
Machiavelli once stated that “the end justifies the means”; should we follow such a doctrine or should we be concerned about the means?
Do you think that the means are more important than the end or do you think that the end is more important than the means?
If you accomplish the intended moral ends; can you live with the knowledge that you reached your “respectable moral ends” through immoral means?

Does it make a difference when your immoral actions affect others? Is it more justifiable when no one gets hurt?