I have a drawer tab (closed) on the left edge of the screen. Where are the images kept as I would like to change how it looks when open and closed.
I checked C:\Program Files (x86)\Winstep and the only folder in there is one called Help
I am using the trail version at the moment to see how I like it.

As a complete Newbie to Winstep Xtreme, at this stage I would only recommend that you change the Drawer's appearance by changing its theme. Please note that the drawer tab appearance when minimised vs. when activated is defined by the theme in use.

I thought it would just be a matter of replacing the open and closed images with the ones I want to use. So not as simple as that.I had in mind using an old desktopX skin I use.

Not as simple as all that, no. The new images would have to be of the exact same dimensions as the ones you want to replace in the theme. I would suggest leaving any modifications to any theme well alone until you get to know the app better. And of course you would need at least some proficiency in creating and modifying graphics files.

As Nexter said, the appearance of a Drawer can be changed by changing its theme. Same for GridStacks, as both are basically different expressions of the same thing and thus use the themes/bitmaps originally made for shelves.

One thing to note is that each Drawer, Grid Stack and Shelf can have its own individual theme, if you want, instead of just sharing the same monolithic global theme.

So, try searching the hundreds of available Winstep themes for one where you like the shelf theme, download it, and then apply that specific theme to the Drawers in an individual base.

This small Themes Tutorial might also help to understand better how all this works.