i got my pc reformatted and now my dvd player wont play. it says i need to install a dvd decoder.

1.so where can i find it (free but great video quality)?
2. i have this software called Xvid on my other computer. is that what i need to get the dvd player to work?
3. whats the difference between DivX and Xvid?


Thanks for you help guys ;p ;p