You need to know your PC IP address to put it in the .ini... for example if your PC has an IP address 188.8.131.52 you open command line on the PC (cmd) and launch ps3serv
ps3serv d:\downloads 12345
then put in options.ini
Don't forget to use quotes "" if you share a folder with spaces in the name, like:
ps3serv "d:\My Music" 12345
Sharing a root folder may be too slow, because the server will scan 8 levels deep to find all the files/folders and to send them to the PS3.