|Well, to use straight HTML/JS, you'd need to convert it to a CSV - JS won't open an XLS. |
But when converting to CSV (File / Save As...), you'll loose all formatting - i.e., bold, font styles, formulas, etc. It'll just be the data.
There's serveral CSV2Table tools for jQuery, here's one I found:
If you really want to read an XLS, you'll need to use some server side scripting technology (PHP, PERL, or .... .NET) to convert the XLS.