Bingo ! Found it !
You were right. The path to the phpdb.php was incomplete. The URL should have included the full path...
url: '/Full Path Here/phpdb.php',
Now for my next problem...the serialize is too non-specific...my database contains a new row ok, but an empty cell for petname
I need to "grab" petname from the posted array? I'll have another think
Thanks so much for all your help.
Also, for the benefit of others... I had to add "return false" to the Ajax, to stop the page from reloading, e.g.
var petnamevalue = $(this).serialize();
alert("Data has been submitted to the Database");