when you save an image from powerpoint, it ends up being 150dpi. To make a higher resolution brochure, you need to make your page twice as large as the actual size you want. So if you want a 5x8in image at 300 dpi, make your powerpoint page 10x16in. It still ends up being around 277dpi for some reason, but that is high enough. 150 might do the job too. 300 is ideal, but often less dpi looks the same.
To get rid of the guides, you will need to delete the image. I'm guessing your guide is on the powerpoint file as a .jpg. Just click it & delete. Then group everything else & save it as a jpg.
Powerpoint really isn't for designing things for print. I used it alot for my projects, because at the time it was the program i was familiar with.