phranque - 7:31 am on Feb 16, 2012 (gmt 0)

welcome to WebmasterWorld, rugrat!

in most cases the issues you are pondering are handled by the db server.
you should probably read the mysql reference sections on table locking and concurrent inserts.
MySQL 5.0 Reference Manual :: 7.7 Locking Issues:
http://dev.mysql.com/doc/refman/5.0/en/locking-issues.html [dev.mysql.com]

also from your description it sounds like you are relying on related rows in separate tables having the same primary index values.
if this is your intent you probably want to use something like a foreign key to cross-reference between tables.