Lars Magne Ingebrigtsen wrote:
> I've now tested gnus-html under Emacs 22 on a "clean" machine, and I
> found a missing require, but nothing major...
[...]

`set-process-plist' and `process-plist' that gnus-html.el uses
are not available in Emacs 21 and XEmacs.  Aren't they something
like the following?