S4 : package creation

Hi the list,

Using S4, how can we create a package? In "S4 Classes in 15 pages, more 
or less", they put all the classes definition in a function that will be 
called at the opening of the library and they add "by hand" a Rd file. 
Is it the only way ? Is there something like "S4.package.skeleton"?

Thanks

Christophe