From what you say, it is very probable that you have a Mac.
Even if you don't, dld and install VLC (google Videolan or VLC to find the official site) which can play most movies.
You probably can't play them yet because you are lacking those damn codecs that are there to make sure everyone gets more confused and has a bad computer experience.
iMac G4 OSX 10.3.9
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps
"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-