Exporting JPEG in Adobe Illustrator CS

I just realized that if I want to export a JPEG filea from Adobe Illustrator CS so that I can maintain the document size (800 x 600 in my case) and have the JPEG file important in PowerPoint at ease (without too much of resizing mess), I need to make sure that there's no hidden object occupies the area outside of the document. Such an obvious tidbit, but I was failed to recognized it and was fustrated myself my exporting a bunch not-so-right-in-size JPEG file.