(Note that there is no `scroll-margin' control in XEmacs.)

BTW, another problem related to `scroll-margin' seems to have
been solved in the latest Emacs 22.0.50 and 23.0.60:

>>>>> In <b4m4pbs7c2e.fsf@jpl.org> Katsumi Yamaoka wrote:
> The problem is, in short, that the cursor in the Gnus summary
> buffer jumps to a subject line that is not for the article being
> displayed just after selecting the article by the `g' command, if
> `scroll-margin' is a non-zero value (actually it is 3).  You may
> need to have many articles in threads and to expand the summary
> window to a certain height.

Regards,