Its possible, with the right cable, don't buy retail:
I realize how old this post is, but I want to confirm that it is possible to use PC speakers on a television. To audiophiles: anything is better than using the sound bar that comes with a TV, even computer speakers. My current inexpensive setup is that I'm running my desktop on a Sony kdl32l4000 HDTV with a VGA cable, and computer speakers hooked up to the computer. Cable box and Wii still operating on the same speakers using its appropriate connections (wii=component, cable box=HDMI).
The key to all this: An auxillary port on the speaker control I have, a headphone to composite cable for audio (aka headphone to red and white), and a fixed audio out on the TV. Basically, the headphone end goes into auxillary port, the red and white goes into the fixed audio out. The rest you hook up like you normally would. Set the volume on the TV speakers all the way to 0, or just turn the speakers off in settings. Heres the thing though: volume control will be all software if you want to use the remote (my speakers have a volume knob on full). You will use the cable box's volume feature to control the volume, DVD players or Blu-Ray players you will use its volume feature, computer has its own, etc. My only problem is with the wii, where there is no way to adjust the volume without walking up to the knob. But whatever, not too much of an inconvenience there.