I had the exact problem. Here's how to do it:
1) First go to Control Panel, then look for "Folder Options" there check the box "Show hidden files"
2) Go to the Personal Folder (Windows 7), now there is a folder called "AppData", open it, and follow this path - "Local/SWTOR/swtor/settings/" there look for "client_settings" file, and open it with Notepad.
3) Now change these 2 lines
OLD
Height = 1200
Width = 1600
NEW
Height = 1050
Width = 1680
1680x1050 is the native resolution for my monitor, in your case just set your monitor's native resolution. then save the file, and play the game