In photoshop I'd like to be able to use my wacom to draw straight lines by the click-shift-click method but the brush size changes from large to very small as it would it was pressure related. Has anyone found at solution for this problem?
Disable the Shape dynamic on the Brush Panel.
I believe it's on by default.
It's the Size Jitter there which causes a brush to change size as you paint.
Here's a video that goes into the details, but basically you need to disable shape dynamics. There's a button in the command bar that does that:
You can also disable it in the brush settings panel by setting the size control to off:
