Turning white/gray into alpha-transparensy

so my problem is that I also draw on paper, and now as I want to edit stuff on Photoshop CS2 I find that I am not able to easily and smoothly make the image transparent through a grayscale image of the image...

I hope that explains my problem good enough... -.-'

Hey Erska,
1. Press [Alt+Ctrl+~] to load white area as selection
2. Press [Shift+Ctrl+I] to invert the selection
3. Create a new layer [Shift+Ctrl+N]
4. Fill the selection [Shift+F5] with black color.

NB In case the strokes appear too thick, undo the filling [Shift+Ctrl+Z] > edit the selection (e.g. Select > Modify > Contract, Feather, etc.) > Fill it again

thx <3
as I have an finnish keyboard layout the button combination is ctrl+alt+1 ^.^