Even a plugged USB drive to PC and shared via SMB doesn't need to be defragmented.
Anyway it isn't bad to have files unfragmented even if it is not required for OPL, but your OS ( MS in this case ) will have better handling for the files ( MS is slow if you have too many fragmented files, it perform better with unfragmented files ;) ).
Giving read access to your shared folder for "Everyone" with password protection set to off in Win7 is sufficient for use with OPL. I did this before switching to secure share. In WinXP Pro it was also enough ( Iirc you had activate Guest account also but why i don't know, MS is sometimes a miracle ).
In theory someone who knows your ip and know how to get past your router/modem could access these filesharing with both methods.
In some games it works flawless and in some other games it stutters. In later revisions you can try some compatibility modes which can stop stutter for some games even if this mode was meant for other purpose ( compatibilty for game(s)).
And we are glad you got it working :)