Have you considered buying a Macintosh? I strikes me that the areas you are interested in, music, video production and photo editing, have long been considered the platforms strong points.
The free applications iTunes and iMovie are great for entry-level music and video editing respectively, while Apple’s Emmy award winning Final Cut software is widely considered one of, if not the, best nonlinear video editing applications available. Also, Adobe Photoshop is a Macintosh mainstay and can handle any photo editing task you throw at it. You could even run the free Linux editor the GIMP on Mac OS X with the new X11 app that Apple released.
Plus, all Macs come with equipped with FireWire, the standard for digital video, and the only way to connect an iPod (my personal favorite mp3 player).
Now, obviously if you have already invested a fortune into windows software, or need to play all of the latest video games the day they come out, you should probably stick to a windows system. However, for the areas that you are interested in, I would strongly suggest looking into a Macintosh.
If you do get an apple computer a dual processor power mac will probably be best for video editing and photo manipulation.