I've thought about this concept before. Adam and Eve didn't know right from wrong; however, they were commanded not to eat; however, they were also commanded to be fruitful and multiply, and they knew they could not do so without first eating the fruit which gave them the knowledge. Does this mean they were forced to eventually eat the fruit? The temptation would seem very great, plus God basically gave them contradictory commandments. It's almost as if they had to sin. I think the type of knowledge they would gain from eating is different than the simple commandments of God. Every person has a consciense, and the fall is what gave us that consciense, which is why after the fall... "And the LORD God said, Behold, the man is become as one of us, to know good and evil: and now, lest he put forth his hand, and take also of the tree of life, and eat, and live for ever:" God's commandments gave them knowledge, but not real knowledge of good and evil. They had these two commandments and they knew they were supposed to obey God.
Anyway, you guys don't realize what a big topic you've brought up. I won't get into it right now, but maybe later. Lots of stuff gets involved, like free will. Sweet. I love these kinds of discussions.
What was the original topic here? Oh yeah. Any sin will keep you from getting into heaven, but some sins are harder to repent for. That's the difference. The difference is there because of this knowledge of good and evil. We are initially less tempted to kill someone than to, say, cheat on a test. The cheating is the lesser sin partly because God understands the temptation and our weak will to it. If we commit murder usually we feel great amounts of guilt. This is also tied to the simple severity of sin as it offends God. Murdering one of his children is far worse than cheating on a test, but both are sin. This isn't an easy topic either, but I think I got my point across.