Single-click always opens documents

I have become increasingly irritated with the clicking on my laptop (Inspiron 1501). Even though XP is set to open with a double-click, I find when I drag and drop (I have to do this a lot--I have My Docs on a separate partition) that single-clicking to select, will often open the file. This is irritating and occasionally time-consuming as well. I have gone into the Control Panel and have a decent array of options with the touchpad (synaptics) and mouse controls, but I'm really not sure what to do. I tried increasing the sensitivity on the touchpad to "heavy touch" but that didn't solve the problem, and made me press significantly harder on the touchpad itself to move the cursor. This isn't really a touchpad problem so much as a cursor problem.

Almost every forum thread/blog post from a Google search turned up instructions on how to make Windows open files with a single-click. I can already do this (unfortunately) and am trying to get Windows not to.