If you've got many files on your computer, you'll need to organize them in some fashion, otherwise it will be complete chaos, especially when it comes time to find something. I mainly use a Windows 7 desktop and it's really important to find files quickly, without resorting to a Windows Search. Here are some tips.
I use a hierarchical system that works over a multitude of hard drives, thanks to the Document Libraries of Windows 7. Document Libraries allow you to associate a folder, like Photos, with different locations, like D:\photos and F:\photos, making them easier to access. For example, you could store your data over a number of drives, but access them in an easy fashion, thanks to this system.
To start out with, I name my drives in sequence. So the C:\ drive will be 'xxx1'. The D:\ drive will be 'xxx2, and so on. Then, I have major categories, like Documents, Pictures, Music, Video. As the need arises, I create sub-folder within this system. For example, I'll put all of the photos that I take into a folder named My Photos, which is in the Pictures Document Library. This is easy to do in Windows 7. You just need to add another location to the folder in your Start Menu. Each series of photos go inside a folder. You get the idea.
I'll do the same for TV shows and movies. If I have many episodes of the same show, I'll create a folder for it. Music is separated into different genres. This makes it easy to select what to listen to. I tend to use Windows Media Player to play my tunes. I've used other software, but WMP is fine for almost anything.
By using this system, or a system like this, you can easily spot duplicate files and address this if it arises. This also means that I rarely search for a file, because I just know exactly where to go to find it. I display files in alphabetical order or the date when they were last modified in my work-related folders or photo folders. It makes it easy to see on what you were working on most recently.
What file organizing system do you use on your computers?