multistep form and selectors

Hi .
How is it possible using multistep form at each step the selection of an option to reduce the selections of the next form step taking values from the taxonomy module.
If for example i have a selector at the first step that says
Please choose a continent then at the next step if i choosed europe it will only lists the eupoeans countries and then it will provide me with a new selector that will inform to choose a city from this country.
I know it looks like a taxonomy but i have nodes ( content types for this ).
So
Continent
Europe ===> submit form step 1
U.K
Spain
Greece
Italy ===>submit form step 2
Roma
Milan
Torino====> submit form step 3
etc
go on with adding the rest of the data.