You have created a custom theme called my_theme within the default package and want to override the native
template file /page/lcolumn.phtml. You will need to place the file in the following structure:
A.
app/design/frontend/base/my_theme/template/page/lcolumn.phtml
B.
app/design/frontend/my_theme/default/template/page/lcolumn.phtml
C.
app/design/frontend/default/my_theme/template/page/lcolumn.phtml
D.
skin/design/frontend/my_theme/template/page/lcolumn.phtml
E.
skin/design/frontend/base/my_theme/template/page/lcolumn.phtml