+200 lbs too
These guys have said it all, this really isn't a job for Joe DIY unless he plans to spend several days at it along with a couple strong pals. This is no joke. =) It's a lot of heavy work and requires some knowledge.
Some points to ponder are that the tub is also wider than the walls OUTSIDE the tiled tub surround -- as will be the equivalent new tub -- and doing this tub swap may require removing the sink, toilet and door frame as well.
The old tub can be broken up with a sledge hammer and taken out in pieces, but the new tub has to be squeezed in. Which means removing enough tile and board behind it to deal with tipping the new tub in at an angle -- one end slightly higher than the other.
An old cast iron/porcelain tub weighs about 200 lbs and even the pieces are heavy -- yes, those broken ends are sharp.
I'd say this is a safe DIY project only is you have another bathroom -- this one will definitely be off-line for a while.