Ok! success: here's what I did.....
As I wrote above, the current mysql version is 5.0.0_2, both client and server packages provided by 5.3 freebsd.
I got php5.0.3 from the main php site and built it with this statement:
./configure --enable-fastcgi --with-config-file-path=../conf' --enable-discard-path --disable-path-info-check --with-mysql=/usr/local/bin/mysql
copying the php bin over as the how to says and Poof! got right into the new PostNuke install. Have yet to copy my exist site & data over, but I think this was the hard part. Still using the original php.ini, so I expect my next hurdle will be in there somewhere.
Thanks for the assist. So far, so nice...