Got a router? How's it all set up?
Use
Windows Media Player 11 /
TVersity /
PS3 Media Server on the laptop to stream your media to the PS3. Easy
WMP11 will stream only the formats it knows. You can edit the registry though to enable WMP11 streaming of .mp4 & .m2t files.
TVersity & PS3 Media Server will stream more containers & codecs than WMP11, & will transcode on-the-fly anything the PS3 itself does not support.
I used to use WMP11, tried TVersity briefly, & now just use PS3 Media Server.