for me, it's messed up in both IE and FF. maybe my version is different for IE. i just went to your xanga. i'm checking your source. you haven't fully changed everything.
only keep # if you're replacing with color. there are 7 zeros for background color.
CODE
/* edits the date */
div.blogheader, .caption
{background-image: url();
background-repeat:no-repeat;
background-position:center;
font-family: Georgia;
text-transform:bold;
font-size:#14px;
line-height:#px;
font-weight:normal;
color:#D93A43;
letter-spacing:2px;
background-color:#0000000;
text-align:center;
border:1px solid #D93A43;}
edit the border and font size
CODE
input, select, textarea, iframe.htmleditor, .textfield, .button {
/* this edits the buttons, dropdowns, etc. */
border: #px solid #000000;
font:normal #9px georgia;
background-color: #000000;
font-color:#D93A43;}
edit the border and the width
CODE
table.blogbody {
/* this edits the other the place where the blog is */
background-color:transparent;
family-font: georgia;
BORDER: #COLOR CODE #px solid;
width:###px;} /* <-- The width for this should be around 5-15 pixels less then the width for your blog's div layer. */
edit the font color, font size, font family, border color, border width
CODE
table.left th {
/* on your menu module, this edits the title part of it */
/* like BLOGRINGS, POSTING CALENDAR, etc */
background-image: url();
background-color:none;
color: #COLOR CODE;
font: bold #pt FONT FAMILY;
text-transform: none;
text-align:center;
border: #COLOR CODE #px solid;}
edit the background color, border color, border width
CODE
table.left {
/* this edits the menu module */
width:180px;
color:000000;
background-color:#COLOR CODE;
BORDER: #COLOR CODE #px solid;}
edit the line height and font size
CODE
a:link
{line-height: #pt;
font-family: georgia;
font-weight:normal;
color:#D93A43;
text-transform:underline;
font-size:#10pt;
cursor:crosshair;}
edit the font size
CODE
A:hover {font-family:georgia;
color:#FFFFFF;
text-transform: uppercase;
cursor: crosshair;
font-weight:bold;
font-size:#pt}
there don't really solve the whole "mess up" thing, but it does solve the customization.