Hmm, I'd heard that they were going to start charging for some versions. Is that what you are referring to?
On FreeBSD, MySQL is still in ports, so it's as easy as:
$cd /usr/ports/databases/mysql323-server
$make install clean
I think that version 4 is in there to ... don't really know and aren't heading in there to look ATM ....
And, surely if it's still free for FreeBSD, you can get Linux RPM's, etc. Dunno about Windows.
Some folks would also say that PostgreSQL is a reasonable if not better alternative, and AFAIK it's quite free ...