I do this in CS2 wihout any problems.
Select file then New
Enter 21.1cm for the width.
Enter 29.7cm for the height.
Ensure background content is White.

Now open your photo that you want to print.
Make sure it is 8 x 10 by clicking on Image
Then Image size - sizes should be 20.4cm for width and 25.5cm for height.

If all ok then click your photo and drag into your new one your created first and place in the middle.

Job done

Then just print in the normal way.

Hope this helps.
All the best
Paul

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Ever notice that anyone going slower than you is an idiot, but anyone going faster is a maniac!!