Microsoft(Bill Gates) made it! I bet I got the right choice! I was concerned I couldn't buy this upgrade version of Power Point 2007 at first because I had never installed Power Point 2007. However, I was so relieved I could install this with no problem at all; that is, this installation proved to be successful as long as I installed Microsoft Office Personal 2007 like the computer shop staff said. What was better, I could save 1/3 of money! Without Microsoft Office Personal 2007 I would have had to pay about 28000 yen, which is definitely ridiculous! In fact, I used to deal with both Power Point Viewer and Open Office before getting this upgrade version of Power Point 2007. The trouble was that I wasn't able to see my files on Power Point Viewer unless I made presentation files on Open Office. In other words, I had to forward the files to Power Point Viewer after completing the files on Open Office. That was also a waste of time and energy. At last I deleted both Power Point Viewer and Open Office!
I suppose some people may complain their computers don't include Power Point 2007, which they may find inconvenient. But don't worry; this is highly recommended for them. Besides, it's also compatible with Windows 7. Don't miss it!