That's really easy.
All you need to do is to make a transparent (transparent, not white) image in a good image-editing utility (Fireworks, Photoshop, Paintshop, mostly anything except MS Paint) with a 640x480 resolution. Put your image in the corner, where you want it to be in your video, and save the image with a .psd extension.
Now import it with Premiere. It'll ask you which layers to import, check the upper option. Put this image in a video track above all the others, make sure this track is visible, and you're done. ^_^
When the gods wish to punish us, they answer our prayers - Oscar Wilde