No subject

5-10 characters _too_wide_ (so that it won't fit across the available
display and is being "hard wrapped" by the terminal), or something else
about your display is not consistent with what nroff -man is expecting
of your terminal layout.

Given that you report that you can widen the window to make it "display
okay", but need to do this each time around, I'd say that it's most
likely that the correct width is being detected (from the tty settings),
but that for some reason the way it is formatted is not displaying
correctly within the detected width.  (Incidentally you can always
narrow the window again after "man" exits, to avoid the "ever wider"
window problem.)

My two guesses would be:
- character encoding and/or character set mismatch between what you're
  using and what nroff -man is expecting; 

- tab handling issues

(If it weren't for the fact that you report it happens with xterm, then
I'd be inclined to blame it on a lame terminal emulator.  Many of the
new fangled KDE/Gnome/etc terminal emulators seem to handle anything
outside of glass tty and colours poorly.  Even simple things like
scrolling backwards smoothly, which real terminals have supported well for
the last 20 years...)

For the character encoding issues you might want to try:

LANG=C man man

to force it not to try to use a utf-8 encoding for that one command
(several modern distributions will default to assuming utf-8).  If 
it helps try setting LANG=en_NZ and see it that helps too and/or
verifying the character encoding matches between your terminal and your
environment.  (I see these mismatches quite often when ssh'ing from an
"older' Linux install into a newer one.)

For the character set issue you should probably verify that you're using
a fixed with font; trying it in a window started with:

xterm -font fixed &

and see if the same problem happens.

For the tab handling issues you might want to try forcing the pager to
use to a different one and see if that helps; eg

man -P less man

or 

man -P more man

Ewen