OK - one more step, but this worked.
1. Open your Excel spreadsheet.
2. In separate window, open Paint (it's in your Accessories)
3. Copy the cells you want in Excel
4. Paste them into Paint
5. Save your Paint file as a .jpg file (other options may work, but .jpg definitely does)
6. Upload the .jpg file into imgur.com, and you should be able to insert that imgur file you created into your posts here