Nope... unless you have a big button that asks them what they're using. It's a bit like trying to detect if a user is wearing glasses Just out of interest... why does it matter?
... and what would you send to LCD users that would/should be different? You'd not vary the aspect ratio since there are 4:3 LCD's, it's not like sub-pixel aliasing of fonts is in your control unless you are using images for text, which depending on the element is either /FAIL/ or normal aliasing would be close enough... Just what are you doing that it should make a difference?