yep you can do
$query="insert into table1(cols) values (......); insert into table2(cols) values(.....);"
just place the semicolor after every query completion..
While you can do this, you are still preforming multiple queries. You cannot actually write one query with one result to insert against multiple tables unless it is into a View (which are not available in MySQL). Personally I would rather see the return result from each insert than potentially have a fail happen and miss it.