I wanted to know how to create a working one because none of the saves that I create work if you'd bother to read my post and indeed the thread title
Are you aware of the problem of lastsave data overwriting newly added .sav file if you're not careful, as I explained in your GBA roms thread?
Do you understand how to avoid it?
At what point in the game are you trying to edit your .sav. Editing stuff too early in the game can cause errors, I strongly suggest waiting until after Dawn (or the guy if you're playing a girl), gives you 5 pokeballs and gives you a tutorial on catching pokemon.
I had no trouble using pokesav with the USA release of both pearl and diamond, on a dslinker, also an n-card clone.
For reference sake I did it like this:
On DS.
Play pokemon pearl
save the game AFTER I got the pokeballs, had healed my starter pokemon and visited the storage computer at least once.
RESET DS
Play something OTHER than pokemon (this backs up and removes the pokemon save data from lastsav.sdb)
Off DS.
On DS - into USB mode.
Copy the pokemon sav file from DS to computer.
Start pokesav and locate the sav just copied to computer.
Edit away (don't overdo it) - see the pokesav threads on the rom hacking forum for more on it.
Save the edited sav (Its been a while but I recall the 256 size was fine since this is the default save backup size for all n-card clones)
Copy the edited sav to the DS. It should prompt to overwrite. Let it.
Fire up the DS and play the game, now with edits.
It worked for me...