Why on Earth would Internet Explorer in XP wrap the last page menu or category menu item into two lines?

body,html
{
background-color: #003366;
background-image: url(http://www.domain.com/gfx/blue_blend_background.jpg);
background-repeat: repeat-x;
}
#middle {
background-color: #c9ba9e;
background-image: url(http://www.domain.com/gfx/paper_background.jpg);
background-repeat: repeat;
}
#header {
background-color: #c9ba9e;
background-image: url(http://www.domain.com/gfx/paper_background.jpg);
background-repeat: repeat;
}
#pagebackground {
background-image: url(http://www.domain.com/gfx/navbar_background.jpg);
background-repeat: repeat;
}
#catbackground {
background-image: url(http://www.domain.com/gfx/navbar_background.jpg);
background-repeat: repeat;
}
div#menu1 {
background: transparent !important;
border: transparent !important;
}
div#menu1 ul.rMenu li a {
background-image: url(http://www.domain.com/gfx/navbar_background_dark.jpg);
background-repeat: repeat;
border-top: solid 1px #b0a28a !important;
border-right: solid 1px #b0a28a !important;
border-left: solid 1px #cec0a9 !important;
border-bottom: solid 1px #cec0a9 !important;
padding: 10px;
}
div#menu2 {
background: transparent !important;
border: transparent !important;
}
div#menu2 ul.rMenu li a {
background-image: url(http://www.domain.com/gfx/navbar_background_dark.jpg);
background-repeat: repeat;
border-top: solid 1px #b0a28a !important;
border-right: solid 1px #b0a28a !important;
border-left: solid 1px #cec0a9 !important;
border-bottom: solid 1px #cec0a9 !important;
padding: 10px;
}
#pagecatarea {
	height: 67px;
}
img.floatNavLeft { 
	float: left;
	margin: 0px;
	padding: 0px;
}
img.floatNavRight { 
	float: right;
	margin: 0px;
	padding: 0px;
}

It's hard to tell without seeing the site but have you applied the menu related bug fixes?

What menu related bug fixes?
http://dev.smilefortcollins.com

The first two on this page.

I am using Wordpress menus so I guess I won't/shouldn't implement this fix.:
BUGFIX 351-04: Fix sub-menu padding with WordPress 3.0

I did implement this fix, however, already:
BUGFIX 353-01: Fix styling when using the new WordPress menus

I found this snippet and it fixed my wrapping problem:

ul.rMenu li a {
white-space: nowrap !important;
}