A little info about my problem that may help others.
My 8400gs is back (almost changed it), but the thing is that it wasn't related at all with it or the kexts, efistring or nvcap, all I did was modify the AppleNforceATA kext and set:

<key>Serial ATA</key>
<true/>

in the PATA section.
Although I have a IDE HD it gave a huge performance boost to my leopard.

I must give the credit to e-rick from insanelymac.