mysql libraries

[Cloud]

I'm moving servers and I'm going from mysql 4 to mysql 3.

I'm concerned about two things currently.

1.) My admin is telling me there is a problem with PHP not including mysql libraries for mysql 4, so he's sticking with mysql 3.

I know I use function like mysql_connect and mysql_query in my scripts but I don't know if this is using the mysql library or if its just a basic function in php (what would you call it?).

2.) I'm concerned about problems that may occur from downgrading to mysql 3. Anyone have pointers as to what to look for?

Thanks in advance!