Version 1.0 of Microsoft InfoPath originally shipped with Microsoft Script Editing technologies, giving the user the choice of using either Microsoft JScript, which is the default scripting language for a form, or Microsoft Visual Basic Scripting Edition (VBScript). Other Microsoft Office products ship with Visual Basic for Applications (VBA), except for Outlook, which also uses scripting to program with Outlook forms.
The choice of which of the scripting languages you depend on may come down to which one you have had experience with. If you have used Java in the past, you may want to use Jscript; if you have used one of the Visual Basic development languages, then VBScript may be the way to go.
If you're just starting out in developing, you will probably want to use the default scripting language, which is JScript. If you decide to go with VBScript, then you change the default script language by selecting it on the Advanced tab of the Form Options dialog box.
If you want to change the default programming language behind an InfoPath form, you have to do it before the form has any code behind it.
Using a new form:
Create a new blank form.
Choose ToolsForm Options.
Click the Advanced Tab.
Click on the Form code language, ...