how to create a barcode in asp.net

1. Using a special bar code font (try to google for "barcode font free")
2. Render the bar code to an image and display that (try using the Barcode Rendering Frameworkavailable on codeplex)

In response to your updated question about detecting barcode printers:
I think a barcode printer will show up as a regular printer on your system. At least that is how the devices I have played with have worked.
This means that you can detect a specific barcode printer by enumerating the installed printers on the system and looking for the specified device, but in most cases I would suggest that you let the user specify the printer himself using either the standard print dialog or using a custom dialog.

I know a toolkit (Lead tools) that supports writing different types of 1D and 2D barcodes. It has both .NET and HTML5 libraries that might help you on web. You can find more info here.

Barcode

You can get started by seeing the below tutorial:

Writing Barcodes

You can get more details from their support team using this email: [email protected]