By using tabs and the Merge Shapes feature you can achieve what you want.
Let us suppose you want to create the following example. You can use a circle with a picture background and only one textbox. On top of that the combined objects must be resizable. So no fiddling around with several textboxes.
Step 1
Press Alt+F9 to activate the guides which run through the middle of the slide.Click Insert - Shape - select the oval and drag, starting in the intersection of the two guides, using Ctrl+Shift to draw a perfect circle. You can add the background picture now or wait till the end.
Step 2
Draw a textbox that matches the width of the circle. Type in all the text using the enter key after each paragraph. If necessary adjust the the font size, and change the spacing after the paragraph so that the text is equally spread.
Step 3
Now click the dialogstarter button in the Paragraph group, in the dialog click the Tabs button. At the top next to Default tab stops put a low value eg. 0.19 inch, click OK.
The ruler looks something like this
Step 4
Click in front of every paragraph and press the tab key once or several times so that the text aligns perfectly with the circle border.
Step 5
As a last step select the circle and then the text box. Click the Format tab, in the Insert shapes group click the Merge Shapes button and choose Combine. Finally click the Shape outline button in the Shape styles group and click No outline.
Once this last step is done you can move, resize, change the background of the combined shape.