Steve McConnell has a chapter in Rapid Development about
methods of estimating how big a project will be and how
long it will take. He seems to be a fan of
. I haven't tried that, but it would
probably be a good starting place if you want to learn
more about how people try to estimate how much work various
projects will take.
On a related note, your estimates are likely to be
substantially off because of inevitable feature creep.
Steve also recommends watching the movie Bugsy. As he says,
...it's hard not to feel a sense of justice when Bugsy
is finally gunned down for changing his mind too often and
spending too much of the mob's money. :-)