i'm mining with bitminter client with my GPU that is an "ATI Radeon Caicos PRO Prototype" with a speed of 20Mhps.. how long does it take to make 1 bitcoin mining this way
does it worth it?

At current difficulty, if you mine in a pool, you will probably mine about 0.00001406 BTC per week. That means, if difficulty doesn't increase at all, it will take about 71123 weeks (about 1367 years) to mine 1 BTC. Of course difficulty will almost certainly increase during that time. As such, it is quite possible that it will take more than 6000 years to mine 1 BTC.
or how to easily get bitcoins fast for free??? i don't wanna buy bitcoins... 

In case you hadn't figured it out yet, bitcoins are money. As such, what you are saying is:
"How to easily get money fast for free??? I don't wanna earn money...

There is no magic here. You give something of value (product, time, service, etc) and in exchange you get something of value (bitcoins). That's the way the world works.
but i was thinking about mining bitcoins and then exchange it with dollars or ££££. maybe i should sell stuffs and set as payment method "Bitcoins" only. it seems to be the only way to have bitcoins for free.