Julian is correct, although this is an old fashioned saying which isn't used anymore.

It means I will try to do my best to do it. I badly want it and I will try hard to do it. Please, watch this funny educational video by The Teacher. He explains here this phrase as well. http://www.bbc.co.uk/mediaselector/check/worldservice/learningenglish/meta/dps/2008/05/080506_arm?size=16x9&bgc=003399&lang=en-ws&nbram=1&nbwm=1&bbram=1&bbwm=1