The update is available for all registered Pro-53 users in the NI Online Shop as direct download for 29 Euro/Dollars.
Alternatively, in a few weeks the update will be available on CD ROM via postal delivery (49 Euro/Dollar plus shipping). You can preorder this "PRO-53 Update CD RTAS and Mac OS X" in the NI Online Shop as well.
Customers who purchased PRO-53 after August 15th, 2003 (online or from a dealer) can download the update for free - or order a Grace period Update CD ROM in the NI Online Shop for 19 Euro/Dollars.