Repacking .mqo into .mpet files

I decided to try out the 3d modeling for new items, and i managed to edit one of the existing items correctly, however when i tried to repack it into an .mpet file it didn't work, i've tried all tools and also seached in the forum, but found nothing.

Edit: Ok, i kept digging in the forums and found this.

But what is that .pet file? When i first converted Mpet the only file that showed was the .mqo.

Ok, i managed to repack having the old .mpet in the same folder.
But it ended up totally bugged:
http://img33.imageshack.us/img33/43/pangya195.jpg
Does anyone that understand a bit more about this can help me please?

Edit: The final .new file has it's size almost doubled than original .mpet aswell...