Luke, do you watch starwars? Just curious. For 250W amp, it's not worth it. You'll find cheaper home stereo amps vs trying to convert car amp. If however, you have a nice car amp, then it's possible. I've done it. I find it better than buying one of those all in one subs (built in weak amp).
You'll first need to get a 12V power supply from an Electronic store. Try and match the fuses on the amp. You should be able to see it on the amp's case. Connect the POS to the amp's pos and remote terminals, NEG to the neg terminal. Attach the rca cable to the amp's rca input and you're done. Since most car amps are designed for 4ohms, and your home stereos are 8ohms, you're not going to get the rated power. Probably half the rating.