about using dd command to copy hard drives

[D Velez]

I'm using freebsd 5.0 Jan 2003 series

I know that dd is good at copying block devices when they
are at identical sizes. But if they're different sizes will it
copy correctly?

I want to copy my entire freebsd hard disk  which is 6 GB
to a new hard disk at 20 GB.

I read the man pages but still can't understand it.  I'm only a user
not a programmer nor sys admin. If you have any comments or
suggestions, I would surely appreciate it.

Thanks

David