Rebekah,
This little chart is probably the easiest way to see the differences between Arminianism and Calvinism:
http://www.solochristo.com/theology/Salvation/comparison.htm
There is also a very good explanation here:
http://www.monergism.com/thethreshold/articles/topic/arminianism.html
In very short form, Arminianism (at least as it began with Jacob Arminianus - the latin for James Harmon - in the late 1500s/early 1600s) was not that different from Calvinism EXCEPT that Arminians proposed that God had done a work of grace in the hearts of ALL men (prevenient grace) that "sort of" regenerated everyone. Thus everyone was made "able" to choose Christ, without exception. Anyone who did or did not, did so in his own power, since God had already done "His part."
What that means then, is that the issue really comes down to depravity, and goes back to the battle Augustine fought with Pelagius in the early days of the Church:
[b:001f35b87b]Augustinism (Calvinism)[/b:001f35b87b]: Man is totally depraved and dead in his sins. This is the result of the sin of Adam (original sin) which is counted to the sinner as if he had sinned in Adam himself. (Adam is the head and representative of all mankind) He is unable to do any good, or choose God without an intervening supernatural act of God (regeneration). This act [i:001f35b87b][b:001f35b87b]precedes[/b:001f35b87b][/i:001f35b87b] faith and justificiation, since man cannot exercise faith in himself. Faith is the gift of God (Eph 2:8-9) .
[b:001f35b87b]Pelagianism[/b:001f35b87b]: Man is not depraved at all. He is a "blank slate," with each man having perfect freedom to sin or not sin, to do evil or not. Adam's sin is only an [b:001f35b87b]example[/b:001f35b87b] that man can choose to follow, or he ould follow the example of Jesus. No supernatural work of God is needed to save man, he simply follows the example of Jesus in his own power. This is the de facto view of liberalism.
[b:001f35b87b]Semi-Pelagianism[/b:001f35b87b]: Man is depraved, as in Augustinism, but God has already done a supernatural work in all men to remove the effects of that depravity. Salvation now totally depends on man, and the choice that he makes. God has put man into the position described by Pelagianism, but it took a work of God to get him there, and he is either more or less likely to sin (depending on how "Pelagian" the semi-Pelagian is, and how "un-Pelagian" the semi-Pelagian is.
A really good book to read on this (and other positions) is Warfield's [b:001f35b87b]Plan of Salvation[/b:001f35b87b]
I hope that helps.