asp:Label controls typically don't emit the display:inline-block Style, you may want to check your associated Skin (skinid="rs100") to make sure it's not inserting things into the Style or removing the Width attribute (width="100px") from your Label - ASP.NET might automagically render the style (display:inline-block) when a width is associated to a Label.
asp:Label controls emit a SPAN tag which is an Inline CSS Element - a DIV or Table is a Block Element. I don't think the W3C CSS Standards provide a mechanism for setting the width on Inline Elements (like asp:Label, the span) because you'd typically use a Block type Element, like a Div, or turn your Span into a block element (display: block;).
A couple alternatives you could try:
Try using the asp:Literal in place of the asp:Label
Try wrapping your asp:Label in a Div then set the width and align settings on the Div
Try removing [font-names="verdana" width="100px" skinid="rs100"] from your asp:Label and add the following to your CSS file:
.rightalign {
text-align: right;
display: block;
width: 100px
}
Safari 2.0.3., Konqueror 3.5, Opera 9 and Mozilla Firefox are very W3C CSS Standard compliant, however Internet Explorer is not. If you do your CSS / Design development in one of these more standard compliant browsers you'll pleasantly discover that your Design is more cross browser compatible - this often reduces debug time.