Is there a way to draw/paint in a straight line at an angle in Photoshop?

you need a steady hand :)

If you use the paint brush and hold down shift, click then click some where else while still holding down shift it will draw a line between the tow points. It doesn't matter on what angle, it can be diagonal if you want. I don't know why when you did it it only created vertical and horizontal lines.

It's very simple. After selecting you brush, click where you want the line to start. Then, hold down shift and click where you want the line to end. It will draw a straight line to wherever you click next. Just be sure and hit shift After clicking the first time.This is for Photoshop 7, but I believe works in other versions as well.

Yes... using the pen tool.... at some point you would need to define Rulers to be exact with your angle... then fetch the pen tool click on your first dot... then your second dot... then you'll notice a path was created (this works vertical and horizontal too) then you can just right click> stroke path.

Just use the pen tool and set it for 45 degrees.

Yes, just draw the line, and distort it in perspective in filters. Then you can copy and paste and seam the lines.

I'm not sure. I immediately thought of shift, but apparently that doesn't work.

use the pen tool...

PEN TOOL IS GOD.