The best way to migrate a Project from one NLE (Non Linear Editor) program, to another, if there is no built-in capability, such as OMF (used by PrPro to migrate the whole Project into other NLE's, like AVID, etc.), is to Export a file, that the other NLE can Import and edit smoothly. On a Mac, one example of that would be a MOV w/ the Animation CODEC. Then just Import that output file, into a New Project, that matches the specs. of the output file.
With FCP, there are some CODEC's that will not load onto a PC, and some that will ONLY work, if one has FCP installed on that machine. I do not know the CODEC's used in iMovie, but a little research should yield those options. So long as the CODEC used from iMovie is one that PrE can edit with, you should be fine.
Now, there are two ways to go about Exporting a Timeline for additional editing:
- One is to cut very tightly, with Transitions, etc., that one wishes to use. Basically this will be a "finished" video, just needing a little touchup.
- The other is to edit very loosely, not Trimming each Clip much, leaving enough Handles, to do the final Trim in PrE, and then add Transitions, and Effects.
Also note that the Elements Organizer, Premiere Elements file management system, has a tool built into it for transferring your iMovie catalog into the Organizer.
Meantime, you can get the basics of how to use Premiere Elements by working through my free 8 part tutorial series.
Assuming you're on a Mac, it's under the Organizer's Import button, in the upper left of the interface.
It also usually launches automatically when you first install the program.
However, note that this converts the iPhoto catalog to an Organizer catalog. Videos captured by iMovie are not necessarily compatible with Premiere Elements.