What i want to do is:

I can get my hands on a laptop for $300 pretty good nick but unused by my work!
What i want to do is put it in my car!
So i can play MP3's, games, etc. now is this possible?

I mean how would i connect it to the battery etc. Also making sure that it doesnt drain the battery or blow the laptop up.

How could i connect it to my speakers or through the cd player?
Would a sound card do it?

Any suggestions?