First thing ... you have to setup your PS3 to connect with your home network.
Next... find out which IP number has been assigned to your PS3 ('Settings' and then 'System info' If I recall correctly)
Launch Multiman (maybe you should check if the FTP service is enabled in the Settings)
Then, on your Laptop you can try putting something like this on your browser:
ftp://[ip of your PS3]
if you see some folders, then the connection has been established
Optional but recommended, Download a FTP client to do the file copying (Filezilla is free and great)
Hope this help!