Permantently set/alter the user environment path from a program

Hei,

I try to make a small program - typicaly a .bat-fil - that can be
distributed to other colleges and help them ad a couple of filepaths to the
user environment PATH-variable. I know how to do it manually through the
Control Panel/System/advanced.... I also know how to do it temporarily in the
cmd-console. But how can I do it "automatically" and permanently?

Kajw