The text editor can edit .txt and .ini files of any size, with syntax hilighting on ini files for easier viewing. Moving the cursor is accomplished with the d-pad. Page up and down are accomplished with the &l; and &r; buttons respectively. Home and end is accomplished using the &y; and &x; buttons respectively.
To edit text, simply enter characters on the virtual keyboard as you would on a normal keyboard. Use the d-pad to move the cursor around. The spl button switches keyboards to special character entry mode.