When I am combing 1080, 720 and DV what sequence settings should I use? When I use a DV sequence the HD footage doesn't look good, but maybe this is just because it is a preview and it will look better when I render it? The final will be a DVD. Any advise would be much appreciated!

Fill in some blanks here. What is the frame rate on your sequence? What is the frame rate of all your source footage? What do you mean by "doesn't look good"- blurry? Stutters? On the computer screen, or on a preview monitor?

When I am combing 1080, 720 and DV what sequence settings should I use? When I use a DV sequence the HD footage doesn't look good, but maybe this is just because it is a preview and it will look better when I render it? The final will be a DVD. Any advise would be much appreciated!

Are you editing in 16:9 DV? Regardless, why don't you render a small section with all three formats and see how it looks? If you are considering finishing in HD, I recommend using one of the Apple ProRes codecs for the sequence.