MySQLClient 3.x compatible with MySQL 5.x?

[Pecas On Line]

Hello,

I need to have a MySQL 3.x client to be compatible with a new MySQL 5.x
server, is it possible?

What do I need to change on my MySQL 5.x server to allow old clients to
work?

Also, what do I need to change to allow old PHP 4.x code to talk to a MySQL
5.x server?

Thanks,

POL.