This might help, if you're trying to use widescreen in iDVD
If you export an anamorphic 16:9 DV Sequence from Final Cut Pro with the intention of burning a DVD-Video of that sequence in iDVD, you may need to adjust the aspect ratio of the movie before you include it in your iDVD project. This may be necessary because in some cases, Final Cut Pro does not include the widescreen aspect ratio information that iDVD looks for.
Note: This issue relates specifically to DV format files.
Solution
Use QuickTime Pro (included with Final Cut Pro and Final Cut Studio) to adjust the aspect ratio of the movie so that iDVD will handle it as intended. This won't re-encode your movie, so there will be no generation loss between Final Cut Pro and iDVD. Only the displayed aspect ratio will be changed.
After you have exported the movie from Final Cut Pro, open it in QuickTime Player.
If the movie is displayed at 16:9 widescreen in QuickTime Player, there's no need to continue these steps. iDVD will treat the movie as widescreen.
If the movie is displayed in QuickTime Player at 4:3 or 3:2 (not widescreen), continue with the steps below.
Choose Window > Show Movie Properties.
In the Properties window, click Video Track in the Name column.
Click the Visual Settings button.
Deselect the checkbox for Preserve Aspect Ratio.
Change the Scaled Size:
For NTSC, enter 853 x 480.
For PAL, enter 1024 x 576.
Now the movie should be displayed at a 16:9 aspect ratio.
Choose File > Save to save the movie.
Now you're ready to create a widescreen iDVD project that will handle the movie as intended.