From Caret To TextRange Object

in a DHTML Editing control (MSIE), I need to "extend" the caret to the
nearest text character in order to obtain a text selection (and than a
textRange object with the createRange method).

This is needed because I have a set of functions doing operations
within the edit control's rich text. But all the functions need to
start from a selected text (for example, adding a table row). My aim is
to get the things work also if no text is selected from the user. But I
could not find a way to have a selected text starting from the simple
cursor position.