Others have noted some of the distinctions above but a few more observations.
A Pelagian doesn't see Adam's sin as affecting anyone but himself. In general, a Pelagian believes that a corrupt society causes a man to eventually sin and what he needs is self-discipline to resist sin and to live righteously. Grace is an added help but is not necessary. It is enough to know that God has said: "Do not steal..." and man has the capacity within himself to obey. Consequently, justification is not forensic at all but based upon the actual righteousness of the obedient man. A man is righteous because he lives a pure life - on his own steam.
Arminianism on the other hand believes that the Fall plunged mankind into sin and that grace is essential for man to obey/believe the Gospel - at least get him to the point of believing. Grace is seen as extending to all men equally as God, in the Gospel, gives all men a measure of grace to overcome resistance to the Gospel but the man must take the final step of belief. That grace of God is necessary and is like a ladder that allows a man to get to the very top with God's help but he must take the final step. The Arminian is unlike the Pelagian in that he didn't climb the ladder (God placed him on the top rung) but in seeing a capacity of a dead man to even stand at the top of the ladder is still like the Pelagian in denying the necessity for regeneration before belief.
The Arminian will claim that no "work" is being performed because the acceptance of a gift is no work but, in fact, even though they're acknowledging that grace preceded their belief, it will still only a grace they cooperated with and it sees their unregenerated flesh as capable of doing so. What distinguishes the believer from the unbeliever? Not God's grace but man's decision. And because grace can be resisted, this also means that it can be ultimately rejected later on by the believer because he chose himself in and can choose himself out.
Incidentally, the really sad thing is that most Fundamentalists used to be Arminians but what is becoming more mainstream today is that they are mostly becoming Pelagian.
