How can I go about making a scroll bar?

That has a somewhat complicated answer, but basically you check if the mouse is clicking within your scroll bar's current position and whether it is dragging up or down, then modify the position accordingly. You can also check for the mouse wheel if you want.

 

Each time the screen renders, you use the current position of the scroll bar to determine what part of your image to render, or how much of whatever needs to be inside that specific area to render.

 

While for 1.6.4, VSWE's Climbing the Interface Ladder series is excellent and explains very well how scroll bars function (among many other things). I highly recommend it.

 

It would be easiest to follow in 1.6.4 and then update to 1.8 later, but you can probably manage to do it on the fly as not much has changed since then as far as interfaces go.

That was exactly what I needed.  Thanks for the help once again!