>>>Do DVD movies need to be finalized or something to be viewable?
I have a friend who has received a bunch of DVDs (on DVD-R) that are not playable in a DVD player and a DVD drive (for his PC).<<<<<
Yes, they do need to be finalized.
BUT... if they were burned using a DVD burner on a computer, the software typically automates the finalizing. Most of the burning programs automatically finalize at the end of the session. The only exceptions I have seen are ones where you can go in and "de-select" this default, which would be a rare occurrence.
IF they were burned using a standalone DVD Recorder, then that is a different matter. These units (standalones) do not automatically finalize the disc. One usually has to enter a separate menu on the unit, and direct it to finalize, after all recording has been completed. If this step was skipped, that could indeed cause problems on any other player.
As others have pointed out... you can use easily find software programs to tell exactly what is on that disc, and its structure. ISObuster was mentioned above, there are also others.
Also, there are many reasons why a disc might not play in a given DVD player. Finalizing is ONE possible issue, but there are many others -- some DVD players do not play DVD-Rs, some do not play DVD+Rs, some do not like particular BRANDS or TYPES of media; and also, a lot of cheap / horrible media is out there, some of which can barely play in ANY player at all.
-Bruce in Chi-Town