Remove Background

For Photo & Graphics 11: I am creating a powerpoint presentation & using many clip art jpeg. Most have a simple image on white background. I import to Xara, but after adding some minor graphics or none at all, I am unable to remove the original imported white background. In Xara, I used the mask brush & removed background, but upon export & then import to Powerpoint, I still have the white surround. My slide has a texture background. Advice please.