Please clarify some more, are you trying to load the script on some os that boots or have this display stright when it starts loading?
If it's a script (bat file for example) you nead to write it depending on the syntax the os provides, than copy otherwise provide to boot media as you got then.
If its an *early boot* program that does all *before* anything OS related loads including file access it's clearly a boot loader whitch must be written in *low level* (e.g. asm) language. Learn some assembly first.
Even a boot loaded can have its config files that might be compared to as scripts, and you must load that file as on its documentation may say.
If you want a *custom* boot loader that may or not use a script, you nead to program *a lot*, including drivers, I/O, hardware, file systems, etc, so it's nearly impossible job for newbie. But if you're intended to, check http://wiki.osdev.org/Main_Page
If it's a program (not script) that must run on OS after and/or on its loading, depending on architecture you nead to write its code then compile to executable depending on platform. And anyway you still need to learn more programming, as you *won't load* a win32 program in dos, you nead to make it as 16-bit (dos compatible) program.
So is it a script, a boot loader, executable program or anything?