You could try putting it in the <TR> tag, though I really don't know if that will work. Your other option is have the image as a background for the table. But if you're looking to only have it in three cells out of several, you may have to make those three cells their on table within your outer table. If the image isn't tiled, you could just repeat it in each cell.
Slicing will most likely be the best way to go, just ensure that you specify everything. Slice the image precisely in pixels, and then make sure the cells are also the exact height and width in pixels for best results and to prevent stretching the image.