I'm guessing the TV doesn't have a headphone jack. Otherwise, just connect the PC speakers to that.
Otherwise, look on the back of the TV and see if there's a pair of red/white RCA jacks labelled as AUDIO OUT. You may need to consult your manual for a better picture. Most TVs have these, but newer ones have started switching from the RCA jacks to an optical audio output.
If you have the RCA jacks, use a standard AV cable to connect the red and white cables (ignore the yellow cable) to your speakers. If your computer speakers don't have this sort of input, you can get a converter cable from Radio Shack or any electronics store that has the RCA plugs on one end, and a mini-headphone port on the other. Just be sure you get a cable that supports stereo sound. On your TV, you may need to go into it's setup menu and under Audio options, turn off the TV speakers. Some TVs allow you to still control the volume of the external speakers with your remote. Experiment a bit to find what works best for you.
If your TV only has an optical audio output, it's a bit more complicated. You will need to get a surround sound processor. They do make them for PC speakers..but they usually come with the speakers, and cost about $300 for the whole set. Honestly, the surround sound processor itself is probably about $200 by itself - which is the cost of a low end receiver+speakers kit.
If you do decide to go the surround sound receiver route, be wary. Do not buy those "Home theater in a box" (HTIB) kits that have a DVD player. While these will give you surround sound while watching DVDs, 99% of them do not have additional inputs for your other devices - like your DVD/VCR, or your TV. If you do go with a kit, make sure it comes with a receiver, and not just a DVD player with speakers attached to it. You will need at least 1 digital optical input, and probably more so you could also connect your DVD/VCR to it with its own optical audio cable so you get surround while watching movies. (note: TV is only in stereo, so even if you connect your TV to a surround sound system, you'll hear sound coming from the front left/right speakers and the subwoofer - this is normal. some surround systems may have a "fakey" surround setting which just sends the left/right signal to all the speakers but this isn't quite true surround.)