You should be able to. If you can't play them by selecting them and clicking launch in the library window you can try dragging them manually:

1. Find your incomplete folder (the directory path in the library window tells you where it is). If you still can't see it type command F in the Finder and search 'incomplete'.

2. Make a copy of the partial file you want to play (press alt and drag it onto the desktop).

3. Drag videos or mp3s onto Quicktime Player. For mp3s, you can also try other players such as itunes or Macamp.

Drag mp3s that won't play onto itunes Asscoaitor and then onto Quicktime again.

Drag AVI or DivX files that won't play onto Divx Doctor and then to Quicktime.