margin: auto etc and MSIE again

Thanks to the people who helped me with centering a block of text in
MSIE 5.5 in the site I am developing at
http://www.members.iinet.net.au/~abell1/test/index.htm with city.css
at http://www.members.iinet.net.au/~abell1/test/city.css. I think I
have that under control now, though I won't be able to test it until
Monday.

But the recommended technique of enclosing the block in a div or p
with text-align:centre and using text-align: left in the enclosed
block doesn't work for centering a menu in its div in MSIE 6. If I
use an enclosing element with text-align: centre it centres the menu
in the viewport (not in the div) in MSIE 6 though it works for
Mozilla, Netscape and Opera.

The relevant part of city.css is
#navigation a {
display: block;
text-decoration: none;
margin: auto;
width: 8.7em;
color: #381D7A;
background-color: #AABADD;
border: 1px solid;
border-color: #FFF #036 #036 #FFF;
padding-left: 0.2em;
}
This works well in MSIE 6, Mozilla, Netscape, and Opera, but MSIE 5.5
puts the menu flush against the left edge of the viewport.
How can I the menu options to centre in the navigation div in MSIE 5.5
and MSIE 6?

Thanks in advance, Alex