'Men' Mom -- Charlie and Ashton 'Are Totally Different'

Holland Taylor has been working with Ashton Kutcher on "Two and a Half Men" for a few weeks now -- and she says there's no comparing him with Charlie Sheen ... they're just too different.

When our photog asked if Ashton could fill Charlie's shoes, she told us, "No one can fill Charlie's shoes. He's not trying to fill Charlie's shoes. He's being Ashton! They are both delightful. They are totally different."