Hello

The Programming Environment

Most Office applications use Microsoft Visual Basic for Applications (VBA)
(Visual Basic for Applications (VBA): A macro-language version of Microsoft
Visual Basic that is used to program Windows applications and is included
with several Microsoft applications.) as their primary integrated development
environment, but InfoPath does not. Instead, it uses the Microsoft Script
Editor (MSE) (Microsoft Script Editor (MSE): A programming environment used
to create, edit, and debug Microsoft JScript or Microsoft VBScript code in an
InfoPath form.) as its primary programming environment. This means that when
you develop an InfoPath form, you will not use Visual Basic as the
programming language; you will use a scripting language instead. The
scripting languages that InfoPath supports are Microsoft JScript (JScript: An
interpreted, object-based scripting language that borrows from C, C++, and
Java. It is the Microsoft implementation of the ECMA 262 language
specification.) and Microsoft VBScript (Visual Basic Scripting Edition
(VBScript): An interpreted, object-based scripting language that is a subset
of the Microsoft Visual Basic programming language.). By using these
scripting languages, you can extend and customize the functionality of your
InfoPath forms.

Microsoft Office InfoPath 2003 Service Pack 1 or later allows you to use
Microsoft Visual Studio .NET to write managed code instead of script for form
code in new InfoPath form templates or to add managed code to existing form
templates. To use Visual Studio .NET to create, debug, and build InfoPath
projects that use Microsoft Visual C# or Visual Basic .NET managed code, you
must download the Microsoft® Office InfoPath™ 2003 Toolkit for Visual Studio®
.NET from the InfoPath Developer Center on the Microsoft Developer Network
(MSDN) Web site and install it with Visual Studio .NET 2003. The integration
features provided by the toolkit allow you to use a combination of InfoPath
for form design and Visual Studio .NET for writing and debugging form code.
These integration features allow you to take advantage of such features of
the Visual Studio .NET development environment

I hope this piece of Information helps you