Well, regarding the exhaust, it sounds like there's a hole in it (gets louder as I press the gas), but I haven't had any issues with feeling lightheaded, or sleepy when driving, so I don't think I'm being poisoned (I know you can't smell it, but I'm not having symptoms).
My parent's used to have Mercury Topaz and the sound it exactly the same, however, it doesn't get louder when you press the gas (like it did with the Topaz), but rather it stops.
The light comes on when I'm driving a good distance (about 100 miles to get to my parents) but goes off within a day. =o/ I'm so bad to my car.
At this point, it looks like the exhaust is going to get fixed next month (I get paid once a month, at the end of the month, and I only get $1800/month for rent, bills, food for me, food for kitty, and kitty emergencies).
I can't wait til I get 1) a new job or 2) a permanent job here (oh, yeah, I'm temporary!).