If you create your zscript as a plugin then you put the compiled zscript (the ZSC file) in the ZStartup/ZPlugs folder and your plugin buttons will be available each ZBrush session. All you need to do to create a plugin is to make sure the button paths are the correct form, and that you create the necessary sub-palette (if you need one). So:
Code:
[ISubPalette,"ZPlugin:My Plugin Menu"] //creates a new menu in the ZPlugin palette
//a plugin button:
[IButton,"ZPlugin:My Plugin Menu:My Button","What this button does",
//do stuff
,,.5]// the '.5' is the button width - half a palette-width
[ISwitch,"ZPlugin:My Plugin Menu:My Switch",0,"What this switch does",
// on code
,
// off code
,,.5]
[ISlider,"ZPlugin:My Plugin Menu:My Slider",50,1,0,100,"What this slider does",
//do stuff when value is changed
,,1]