It's true that they're very different. The difference is that (most form of purportedly scientific) creationism actually made substantive claims; e.g. how, when, where, in what context, etc, creation events occurred. ID, by contrast, makes no substantive claims, and virtually promises never to do so. It makes only the evaluative claims that "design" can be detected here and there, that it has something (unspecified as to what) to do with "intelligence," and that at least sometimes it can't be accounted for by "natural causes".
What this means, however, is that any creationist can comfortably and unreservedly adopt intelligent design, and do so whether he's an old earth creationist or a young earth creationist, whether he's a fiat creationist or a progressive creationist, and so on.
So it's not true to say there's no "resemblance". The resemblance is that between say, "Fascist" and "Nazi," or between "Professional" and "Doctor". Or better yet between and umbrella and those who stand underneath it. This is exactly what ID functions as (I believe by DESIGN): a sufficiently vacuous "umbrella" ideology for antievolutionists who are otherwise notoriously schismatic.
The similarity is that when you mock ID you are accused of mocking religion.
The differences result because Creationism begins with the Book of Genesis, an essentially religious approach, and Intelligent Design considers the hypotheses that either the world was created by an intelligent designer or it was not, and considers the weight of evidence on both sides.
By the way, I don't think Creationism is scientific in any way, manner, or form, but I have some sympathy for it. It was an attempt to get religion back into our schools through the back door because our tyrannical courts decided that the freedom of religion clause in the Constitution is meaningless. If it were allowed to teach about religion in school, then it would not be necessary to pretend that Creationism is a science.