Button bars are created within AutoCAD.
VIEW->TOOLBARS->Toollbars TAB->NEW
After the new toolbar is made, select the Commands TAB and at the bottom of the list is USER DEFINED.
Selecting that will show two available options in the right pane "USER DEFINED BUTTON" and "USER DEFINED FLYOUT".
CLICK and DRAG the USER DEFINED BUTTON to the new toolbar.
ONce there RIGHT CLICK on the new button for the popup menu and select PROPERTIES.
The Button properties box is divided into several panes for the button name, button description, button image, and command. The button name is the tool tip that pops up on the screen. You can select a button image from all those available in AutoCAD and then edit it as required.
The command line starts with ^C^C and your command line will look like this:
^C^C-INSERT blockname S (getvar "dimscale"

R 0;
Put in your "blockname", the S presets the scale of this block to the current dimscale, you can put in any scale you wish. The R presets the rotation angle of the block, you can leave this out if you wish and AutoCAD will prompt for the rotation after insertion.
WARNING!!! Keep a clean copy of the original menu in a different directory. It is advisable to make an entirely new menu, for just your custom toolbars, that you can MENULOAD behind the menu you currently use.
Be aware, some shops (mine) frown on customizing company menus. If you want to create your own, on your time, carry on.
Now if you're looking to create the bitmaps for the buttons outside AutoCAD, MSPAINT works okay, but I think PAINT SHOP PRO is better. I usually use the button editor inside AutoCAD.