I don't think there is a good way to make an Excel spreadsheet directly viewable on the web; this may account for the lack of response.

The closest reliable solution I'm aware of is to upload the spreadsheet into Google Docs or similar, publish it (Share > Publish to the web), and put the resulting URL in an iframe on the page. If you'd be doing this repeatedly, a new page type may serve you well; for a one-off it's simplest just to edit the HTML. The only SilverStripe-specific trick there is to make sure there's at least a space between your opening and closing iframe tags (<iframe src="http://YourDocHere"> </iframe>), so that they aren't collapsed into a single <iframe/> tag.

If you want more control, you can save the spreadsheet in .csv format and use CSVParser: http://api.silverstripe.org/2.4/sapphire/bulkloading/CSVParser.html

Hope this helps!