Before I can be accused of putting myself too frequently under Lee's care, let me clear up the nature of my practice. I actually am an appellate lawyer, and so get involved when someone has won or lost at trial and the case goes on to the next level(s) of judicial review. This means I handle many business law issues, but intellectual property is near and dear to my heart. I work with several copyright law gurus who eat, drink and sleep the stuff, and ride in like the cavalry whenever needed. To answer Kevin, though, your first assumption is not quite right. A copyright violation conceivably can occur whenever a copy of a protected work is made. This is because copyright holders have certain exclusive rights in their works: the rights to copy, modify, publicly perform, distribute and publicly display. The kinds of acts you mention in your second paragraph fall within the "fair use" exception - they meet the test for something the law might consider infringement, but for public policy reasons we (through our legislators and courts) have decided certain types of uses, within reason, should be encouraged and not prevented. Copyright holders thus are "deemed" to consent to use by others for research, teaching, comment, criticism, news reporting and the like. Whether something is a "fair use" depends on considerations like how much of the copyrighted work is used and for what purpose (e.g., does the use detract from the commercial market for the copyrighted work). (You also gain certain rights when you own a copy of a protected work - a book, a cd, etc. You can re-sell the item - think half.com - and publicly display it "at the place where the copy is located.")
The DMCA was Congress' attempt to refine and clarify general copyright principles for the digital arena, and impose stricter penalties for certain kinds of copying. (An overview of the Act is available here from the UCLA Online Institute of Cyberspace Law and Policy.) The DMCA primarily is concerned with means of making a copy which did not exist before powerful computers and internet use were commonplace, or which can only be accomplished by circumventing the manufacturer's built-in copy protections. The DMCA also makes certain activities a crime, and thus provides a whole different type of remedy than those available in a private infringement lawsuits. For example, under the DMCA criminal penalties may be leveled against someone who cracks encryption software. ISP's also are shielded from liability for simply transmitting copyrighted material, but made more accountable if they are notified a user's web site may display infringing works. The DMCA is careful to preserve the fair use exceptions discussed above. The end result for your purposes is still the same: exercise caution and common sense. If in doubt, don't do it or definitely consult a lawyer. Your commentary and limited quotation of another's copyrighted work probably would be a fair use. But if you're using a great deal of the work, without the author's permission, in economic competition with the author - have a care. The reason so many copyright cases are in the news these days is that rights holders and users are trying to fit new practices into the old legal structure and see what the courts will go for (consider what *fun* someone could have, for example, with the rule that you can publicly display your copy of a book or a cd at the place where it is located). No one here wants to be the next headline I assume(?), but in fact that's how the law in this area develops. People on either side of the issue decide something's too harmful or just wrong, and turn to the courts for guidance.