Jesse - the only way that you can import via EP is to use a tab delimited text file. You can use Save As from Excel for this but it will only save a "flat" file...therefore you'll need to modify your xls

Also, there is a very specific format to follow, so your best bet is to download your existing products via EP and use that as your template.

If you haven't got product data yet, then just add a test item with as much info as possible to give you guidance.