好久之前写的一偏英文的文章,差不多明白意思就ok了,所以就不做翻译了,呵呵.
You known we can enable the InfoPath form to be filled out by using a browser or client .

But if the InfoPath form template was connected to a web service or Sql Server,you will encounter such issues:

client InfoPath work fine,but in browser mode it will failed when submit the data.

It is due to Authorization privilege. Works great in InfoPath, but when you run a form in the browser, you may be running server-side business logic.  That business logic may want to execute a data query.  Because HTTP is a stateless protocol, Forms Services can’t halt execution of a server-side process and return to the browser in order to ask you for permission to continue. 

Additionally, the user in this case may not be the right person to own the decision about whether the cross-domain connection can take place.  So, this decision is placed instead in the hands of the server administrator who owns security around the form template. 

The basic premise behind UDC files is that in InfoPath 2007 your data connection settings can live outside of the form template in one of these files, and both InfoPath and Forms Services will retrieve the current connection settings from this file at runtime before making the connection.  The UDC file itself is retrieved from a URL relative to the root of the site collection where the form was opened.  This enables lots of cool functionality.

Here give the Brief steps to configure InfoPath browser-enabled:

1.     1.Make sure your form template is marked as “browser-enabled” in “Tools >> Form Options…”

2.     2.Then you need to convert your data connection file to be stored in the DCL(Data Connection Library, you can create this typy list in  SharePoint v3) and enable cross-domain data connections on your server.

3.     3.When you’re publishing, make sure you check the option for browser-enabling the form template on the server.

4.       4.Make sure the form library where your InfoPath form published  is marked as “Display as a Web page” in “Setting> Advanced Settings   …”