Are there any software programs (Windows) that will allow me to draw lines over
any image on a computer monitor? No need to save, just let me doodle
over any image on my screen using my Wacom tablet.

I believe the software that comes with the Smartboard electronic
whiteboard allows you to do this. It looks like the software itself is
a free download from SMART Technology's website. A quote from the
product features:

"Write over applications

"To emphasize or add information to a point, you can write over top of
any application or Web site in electronic ink."

I have seen this in action and it sounds like the functionality you
are looking for. In practice I believe you can write on any region of
the screen.

I am not certain whether the software will function without a
Smartboard connected to the computer, so I am not submitting this as
an answer. However, the Smartboard does seem to work equivalently to a
mouse, so if the software doesn't complain about not having the
smartboard attached, it should do what you need it to do.

Good luck,
smudgy.

The Smartboard software:
http://www.smarttech.com/support/software/sb_win.asp

Product features:
http://www.smarttech.com/sbsoftware/

Google search terms: <smartboard>