If you use images in Word I find it is always best, as you have to start unwrapping them, to insert them into a table so that they keep within their own cell and have the text in the next column alongside. You don't need to have the borders showing but just use table mode for convenience.
However, if by text box you mean you have just a short blurb such as caption, all you should do is when you bring your pic in, click on it right button of mouse down to caption, type your words in the first box where it says Figure 1 (you can't delete that at this stage). Select where you want your caption, top, bottom etc then OK. Once you have got the caption on the screen, then delete the words Figure 1. There is no need to group as you will find if you move the pic, the caption moves appropriately with it.