if you got the script from the links in this thread, there should have been a 'Help' item in the menu. you bring up the menu by pressing the White button

but here's a brief run-down of the controls...
White - brings up menu
Black - deletes characters in the edit line
A - types the currently selected character from the keyboard
B - cycles thru the different keypads
X - moves the cursor (^) back
Y - moves the cursor (^) forward
Dpad - select a key from the keyboard or menu navigation
Rt-Trig + Dpad - scrolls text up, down, left or right