I had a specific issue with adding Flash animations to a Premiere project, which I eventually solved. I thought the tip could be useful to other people.
My project (Premiere Pro CS3) combines still pictures and video, as well as animations designed in Flash CS3 Professional. The target medium is DVD and target display is PAL. I use the export settings described in
http://www.adobeforums.com/webx/.3c054c47/0 #1 with TV standard set to PAL and frame rate set to 25 fps (BTW thanks to Connor Roberts for his excellent advice).
The Flash animations are designed with 5 fps. I used a slower frame rate because the animations did not need a higher one. Most of the frames in the animation are keyframes (the animations represent tracks that unfold progressively on background satellite maps). Initially I used the default settings in Flash when exporting to Quicktime. The .mov files played nicely and the .mov assets were rendered with satisfactory quality by the program monitor in Premiere. However the export to MPEG2 gave a poor result (frames were not displayed or in an erratic fashion). Modifying the Flash animation to 25 fps did not help. What eventually helped was a change in the settings of the export from Flash to Quicktime, namely defining each frame/image as a key frame/image in the video settings.
The resulting .mov files are significantly larger than the ones generated by the default settings. However the resulting MPEG files (after import into Premiere and export) are of comparable size as the previous ones.