For X-Cart Version 4.0.x and 4.1.x, here's some solutions:
Step 1: Locate File: \skin1\main\history_order.tpl and
change the tracking number text box to a textarea.
Step 2: Change the label, {$lng.lbl_tracking_number} via Admin-->Languages to something more descriptive such as: <b>Shipping Information</b>
Step 3: If you need the ability to type longer messages longer than 64 characters, go into the Database via phpMyAdmin and locate the xcart_orders table.
Change the "tracking" field from varchar(64) to varchar(255).
NOTE: Step 3 is unnecessary in X-Cart ver. 4.1.x as the tracking field is already 255 characters.
Optionally: You can also incorporate the
Customer Notes MOD (for version 4.0.19 and earlier, not necessary in 4.1.x branch) and this will provide customers a way to leave you a note and also for you (i.e. the admin) to send a customized note back to the customer whenever you change the order status. The MOD is located here:
http://forum.x-cart.com/showthread.php?t=6888
Robert