If the print driver you have loaded for the printer on your print server is not automatically detecting the additional tray then you can always go out and manually enable it.
To enable additional trays on the print server:
1. Open up the Print Management window
2. Higlight the specific printer in question and right click
3. Enter the Printer Properties area
4. Click the Device Settings Tab
5. Scroll down and expand teh Form to tray assignment
6. Next to Tray 2 switch the status from Not Available to Letter
Note - The status will be greyed out by default, all you need to do is click the status to reveal the drop down menu
7. Click Apply
8. Test