You would have to change the resolution in the video settings on your computer from whatever you have now to xxxxx X 1080. For example, say your currently set to 800 x 600, or 1024 x 768, then you would just bump up the slider until you see 1080 as the second number.
For me 1080 looks terrible with my Nvidia 6600GT higher end card on my 720p projector. It is best to match the native resolution of your tv. You my find a 1280 x 720 gives you better results, that is assuming you have a good video hard. My guess is if it has DVI it should be able to output higher resolutions.
If your on XP, right-click on your desktop, selecty properties, select the Settings tab, and at the bottom you will see where you can change your settings.
