Is it a nutty idea to attempt to drive from Miami to Chicago, going via Atlanta, Washington DC and New York. I will have about 4 weeks from when I arrive in Miami to when I have to be in Chicago - it it at all possible without having to miss anything?

I have driven from central NC to Madison, WI, via Chicago. That takes a day and a half. Sure, you have plenty of time in four weeks. What do you have in mind along the way as far as activities go? We went there via the Smokeys, Ohio, Indiana, etc. The mountain part of that drive is pretty scenic but after Kentucky, the drive was pretty boring. With your route, not knowing much about your interests, I would consider time in Charleston, SC or Savannah Georgia, drive up the North Carolina coast (maybe the Outer Banks), DC, and New York. A few days in Charleson or Savannah, a few days on the NC coast, a week in DC, and a week in New York.

Dan's suggestions are really pretty good. You'd get a more "southern" experience in Savannah or Charleston than in Atlanta. Atlanta is a great city for business, but I swear most of the population is from elsewhere! Four weeks sounds about right. The drive from New York to Chicago will be kind of long through Pennsylvania and Ohio. What time of year will you be traveling?

Agreed. Go the coastal route. Much more interesting. While I think Atlanta is a great place to live, I don't know why anyone would want to vacation here.

Would definitely stop in Charleston rather than Atlanta. Also, there is a really cute town on the coast of NC called Ocracoke, at the southern tip of the outer banks -- you have to take a car ferry to get there, but it's a really great place to stay for a few days and relax.

Best piece of advice I can give you:
drive NY to Chicago at night. Less traffic, miss nothing. It's a 10 hour drive without stops.

In terms of raw driving time, you have plenty of time to do the trip. Miami to New York is about 1300 miles, which is two long days of driving. (I am assuming that you stop to sleep.)
From New York to Chicago, you have a run of about 900 miles plus. I somehow don't think you can do it in 10 hours, without stopping. Driving 90 mph average is a little too much even on the turnpikes and Interstate highways.
All told then you have 4 to 5 days of relatively moderate driving.
That leaves you plenty of time to stop at the various attractions along the way and see the USA. Again, as asked earlier, what time of year are you doing this. January to April could find you ploughing through snow.

Thanks for the tips. We're travelling the East coast in May. Atlanta is a must, the guy I'm travelling with is an Atlanta nut - pretty wierd for an Aussie guy hey!! We have no set plan, just a starting and finishing point. Ideas from other people are exactly what we need, as we have absolutely NO idea what to see.

Unless you plan on visiting Savannah in May, make that a stop on the way to Atlanta. It's on the way. St. Augustine (the oldest city in America) is also on the way and a neat place.

Post back if you need advice on Atlanta hotels/restaurants/neighborhoods and let me know what kind of things you like.