You have to use CSS styles.
In Dreamweaver open the CSS styles window. top left of css window, Create a new style. Call it .bgImageNoRepeat or whatever you want to call it.
In the css panel, select background, then in the image background box enter the url of your image.
Then in repeat box select no repeat.
In the other boxes you can define the position of your image in the cell.
Then go back to your page where the cell is. Get rid of the background image in the html of the cell
(<td background="image.jpg"> change to <td>)
In view mode, select your cell.
Then select the css style you just created in your css window. Then top left css window, select apply.
That will change you html as follow:
<td> will be <td class="bgImageNoRepeat">