performing an sql insert into interbase 6.0 from php 4.0 question.

From php

$sqlstring="Insert into customers(customer_no,company_name)values
(4000,"dave's company");
..execute query($sqlstring)

The previous expression($sqlstring) works from the ibconsol but not
from within php. The problem is the single quote giving ownership in
dave's company. Any idea how one can get around this problem of
single quotes as ownership.