I was testing this feature on all browsers to make sure my changes worked, but selecting a background image on Safari, Firefox and Chrome does not work. I tested this on your demo page, just to make sure it wasn't something related to my settings and I get the same result.

 

Steps to reproduce: 

1. Using either Safari 5, Firefox 4 or Chrome 12 go to http://www.cutesoft.net/example/general.aspx
2. Click somewhere in the middle of the table that's displayed in the sample editor window.
3. Click the <table> selector at the bottom of the CuteEditor and select the "Properties" menu item.
4. Select the Style Builder tab.
5. Click the Background button in the left menu.
6. Click the ... button next to the background image URL text box. 
7. In the Select Image window select an image and click the Insert button.
8. Click the OK button at the bottom of the Style Builder window. 
9. Notice that the background image value was not applied to the table.