This question comes up a lot, so here's a collection of links on the subject:

http://www.dvinfo.net/conf/showthread.php?t=86425
http://www.dvinfo.net/conf/showthread.php?t=28244
http://www.dvinfo.net/conf/showthread.php?t=74566
http://www.dvinfo.net/conf/showthread.php?t=64789
http://www.dvinfo.net/conf/showthread.php?t=73457
http://www.dvinfo.net/conf/showthread.php?t=81211
http://www.dvinfo.net/conf/showthread.php?t=74375
http://www.dvinfo.net/conf/showthread.php?t=87340
http://www.dvinfo.net/conf/showthread.php?t=83937