I think i figured it out (I'm new to modding)
[glow=blue,2,300]MinecraftForge.registerOre("oreCopper", new ItemStack(myCopperOre));[/glow]
put this in your mod's load() method. the above example is for Copper Ore, but you can add anything you want really. though the String parameter should follow the tamplate:
"oreMaterial" or "IngotMaterial" or "gemMaterial"
in general: "typeMaterial"
List of Strings Forge already knows: oreTin, oreCopper, oreSilver, oreUranium, ingotTin, ingotCopper, ingotSilver, ingotBrass, ingotBronze, ingotUranium, ingotRefinedIron, dyeBlue, gemRuby, gemEmerald, gemSapphire, itemDropUranium, woodRubber, itemRubber
