Resource Packs: Textures, Sounds, and GUI.
Quick example of what code would look like:
<<resourcepackname>> --.txt ex: sc2.txt
<Textures>
<Block>
<Dirt>
<img="Textures/new_dirt.bmp">
</Dirt>
</Block>
</Textures>
<Sound>
<Stab>
<sound="Sounds/new_stab.wmv">
</Stab>
</Sound>
<GUI>
<Inv>
<BLPos=750,50> --BL = Bottom Left
<TRPos=1000,300> --TR = Top Right
<invslotSize=50,50> --from top left of inv
<texture="GUI/test_inventory.pdn"> --makes it look like a specific picture
</Inv>
</GUI>
</<resourcepackname>> -- .txt ex: sc2.txt
this would replace stabsound with the custom "newstab.wmv"
and would replace dirt texture with the custom "newdirt.bmp"
and it would make the inventory be at the bottom right of the screen,
with inv slots in it of size 50,50 (half inch) with a size of 5 seperating
the boxes(about 1mm).
example downlaod below:
http://www.mediafire.com/download/0ftcdbe97cs9cs2