best way is converting them with TMPGEnc. Have a look at the tutorials by ChickenMan. Everything you will need is there (trust me).
PS
there are many poor quality movies off kazaa & other p2p programs. Some good ones, but many don't use the proper bitrates or use multiple bitrates (so they can cause a problem), but most times (99%) you can make a standard mpg (VCD compliant) following the tutorials.