time travel problems

in the time machine for sale thread, www.abovetopsecret.com...
but im still wondering, if you did go back in time would it be possible to change anything, i ask this because if you changed something in the past in the new present you wont need to travel back in time to change it so would this mean you didnt change the event in the first place?
also if i went back in time to say when adam and eves era and eve 'liked' me more than adam would i be born??
these questions make my brain hurt can anyone help
i ask this in education because ive always been told i souldnt worry about time travel because what ever happens someone will work out these paradoxs who are these people?
edit;typo

[edit on 26/10/05 by mik0001000]

[edit on 26/10/05 by mik0001000]

First off, read Stephen Hawkings' "A Brief History of Time"
Second off, no offense, but you must not know a lot about science if you believe in Adam and Eve
Lastly, see the movie, Donnie Darko