I guess you are using vanilla Fsod, all you need is JPEXS Free Flash Decompiler.
First of all, open the client swf with it and go to 'binary data' tab, and export 'Ghostship.xml' or something like that :P
Open it with your favorite text editor.
Copy the type of item you want to add (for example if you want to add a shield or something, copy the code for a pre existing shield)
Change the attributes the way you want, and importantly change the name and 'id' to something that wasn't already used.
Save it, and in JPEXS go back to Ghostship.xml and 'Replace' it with the new file.
Save the swf file and add the created item to your server's dat1.xml (server folder -> db -> Data)
Profit!





Note: Once you get used to this whole pserver stuff, try shifting over to AS3 Client (WintersQ made an awesome tutorial on this), it'll make editing and adding stuff a lot easier
