It is impossible to know till its actually happening to you! would be nice if it was just period pain the whole time though...you know, i read somewhere that 5% of woman dont have very much pain atall.....oh to be that 5%!!! (not sure how true that is btw)
Something that got me threw the first few hours was just saying 'good pain, good pain' over and over!! have you read that book by juju sundin (someone will know the name, ive forgotten...birth something) . was pretty good for me.

ETA: its called 'birth skills'...i googled it