Wont take gas, any thoughts?

I have the V8 with 125,000 miles......the car wont go over 10 MPH now! I can start it fine, idles fine but when I give it gas it makes rattles above 2,500 rpm but takes gas when in park, as soon as I put it in drive and try taking off it just simply will not take the gas or gain speed. No back fires and dont try to die........it just wont accelerate. All guages read fine except the check engine light is on........but I cant drive it to have the code pulled, without getting run over. Any thoughts?

Thanks a bunch!

What do the "rattles" sound like?
Where are they coming from?

What year is the car?
Is the oil new?
Is the transmission oil clean, or does it smell burnt?

Later

hello,

with the rattles and the lack of power, but fine idle and the check light being on, it really sounds lik you need to have the catalitic converter checked. my parents had a similar problem with their cougar and i have seen it on a few cars in the past. i think if it need to be changed you should be able t get an O.E.M. one for around $80.00. well i hope this helped.