Iron_bass,
I'll never try to talk you out of buying more gear
D), but I want to make sure that it'll do you any good.
If your PC speakers worked with your PC before, then they will be able to play a signal coming out of the TV if it is there. You just need to make sure that everything is hooked up correctly.
I don't suggest that you connect the center speaker jack to the TV. Connect the jack for the front left/right speakers. Make sure that the computer speakers are otherwise hooked up normally (to make sure that you have them powered up and are working the volume correctly). I suggest that you connect the speakers to your PC and play something (like music) just to make sure they are all hooked up correctly. Then, turn off the audio from the PC (at the PC, leave the speakers on), unplug the front left/right jack from the soundcard, and then plug that jack straight into the TV output jack.
It's also possible that the TV audio out is variable, so you'd have to turn the volume up on the TV to hear anything from your PC speakers. If you can't turn off the TV speakers, that would be a very bad design...but it's possible.
Anyway, if there's no signal coming out of that TV, then a receiver isn't going to do you any good. Your PC speakers could be hooked up to an iPod and work, so they'll tell you if there's a signal coming out of that TV. They are just powered speakers.
Adam