Driving in America - how hard?

[sebhaque]

I'm off to the States next week for work - I can't say I'm looking forward to it. While I've been over a couple of times, I've never driven over there. To anybody who's had experience - how different is driving in the US compared to here in the UK, and is there anything I should pay particular attention to? I think I'm getting an automatic (not my choice!) so I haven't got to worry about winding the window down when I want to change gear.

I'll be in Indianapolis if it helps.

TIA

[sebhaque]

Thanks for the responses folks I'll get to reading!