I would like to incorporate a frame that loads data from a webpage (Windows platform), but don't want to go into writing a web browser widget. If one doesn't exist, any ideas on what it would take to create one?

You appear to be asking for a Tk widget that renders HTML?

If so, what your are asking for is a Tk Web Browser.

With all the complexities of interpreting multiple standards of HTML(1,2,3,4,5), XHTML, XML, css (1, 2, 3), Javascript (of various flavours), Plug-ins (of a multitude of flavours); not to mention handling Bad HTML, XML, css etc.

In a nutshell, the answer to "what it would take to create one?" is: $millions.

There is an MS Web Browser control, that can be embedded within other application (C, C++, C#', VB), and theoretically could be embedded within a Perl application via Win32::API and/or Win32::OLE. But trust me, as someone who wasted many tens of hours trying to do useful things with this, it is a hell of a lot of work for very little reward, due to the significant limitations of both the interface and IE. The control is essentially IE-in-a-window-via-OLE. And that's before you try and integrate it with Tk, which is a world of undocumented magic all of its own.