I think my engine is dead
 

Ok here's the deal. This past weekend I spent about 50 bucks on regular stuff like spark plugs, new hoses, feul filter. I thought that my car was misfiring so I thought that new spark plugs would help that. So I went out and bought NGK spark plugs and it ran extremely well. I live about 50 miles from my dads house which is where I did this. I got hom and let it ran around in my girlfriends car b/c she gets better gas milage. So I start it up about 10:00 pm to go but gas in it and it runs good until about five minutes later then the idle drops to about 100 rpm ( no not 1000 - 100) it doesn't die it just sets there then I start going i turn the wheel and it dies. I press the breaks and it dies. I don't know what to do so any help would be great.
Thanks