I am often amused and frustrated at how people get the 3 general types of intellectual property mixed up. The most commonly confused are Copyright and Trademarks. Though I do often see people confusing Copyright and Patents as well.
So without further ado, here is a brief overview of the 3 types of intellectual property, starting with the most common; Copyright.
Copyright is your ownership of any creative work, for example anything your write is owned by you. You don't need to do anything to copyright your work, the moment your create it, its yours. Your work is yours for life, and also into your death the idea being to provide for your dependents). In most countries you may chose to release your work into the Public Domain (give up any claim to copyright on the work), any work who's copyright has expired (old books, old music etc) are also said to be in the Public Domain. Any work in the Public Domain can be used for any other purpose (within the law of course).
In recent years the large media companies in the USA have worked to have the period of copyright after the death of the creater extended, so as to extend their own control over those created works (most of those companies require the works to be signed over to them for the full period of the work.)
For those of you who with with copyleft style licencing or the like, remember that this type of licencing applies only to works that were first copyrighted.
A trademark is a word, phrase, logo, or combination of those elements that is used to describe something as your work. While there is no requirement for the registration of trademarks it is easy to enforce a trademark if it registered.
The most commonly confused thing I see about trademarks is the idea that no one else can then use that trademark for anything. This is almost completely false. A trademark only applies to the industry in which it is used for. Example; a company who only deals in computers, software and portable electronics can't enforce their trademark on a company that doesn't deal in any of those areas, say a clothing line.
Unlike other types of intellectual property you MUST defend your trademarks if someone is infringing or you risk losing them.
Patents are the ownership of a new, innovative and useful idea (originally for a product or product component and now for processes as well) and were designed to allow public access to designs and ideas that might otherwise have died with the designer (as the designer would otherwise not want to share the idea for fare of having it stolen).
Patents can only be used to stop others stealing your ideas once they are granted by your national patent office, however you would normally be able to work out retroactive agreements to the date of application if someone is infringing on your patent.
To patent something it must be the first idea of its kind, there can be NO 'prior art'. Additionally patents are only granted for a limited period of time, normally about 20 years. After this time the idea is available for all to use. Also patents can not be used to protect mathematical models (Aside: why then can you patent software algorithms?), schemes or some other purely mental process.
Some countries, such as Australia, have additional types of intellectual property with different protections. For more information on this lookup your national intellectual property laws.
Conclusion and Disclaimer
Well I hope you all fount this insightful and learnt something form it, and to finish up i would just like to let you know that I am not a lawyer and what I have written here should not be considered legal advice, or even completely correct. If feel your intellectual property has been infringed upon I suggest you go an talk to a lawyer. If you are simply looking to protect your work, look up your national intellectual property laws, and then if necessary speak to a lawyer or your national intellectual properties office.