Yeah it is far easier for Forge.
Just put the texture in your mod jar.
To reference the texture and attach it to an item or block instance, just do: myItemOrBlockInstance.setTextureFile("/myTexture.png");
Change the "/myTexture.png" part to be where it is in your mod jar file, such as if you have it in a subfolder of "my/mod/and/whatever/myTexture.png", then in the setTextureFile call just do: "/my/mod/and/whatever/myTexture.png"
Please do not be showing ModLoader stuff here if possible, those ways are generally broken and more difficult to use. In the case of ModLoader.addOverride, that is horribly broken. There are a very limited number of sprite indices and they get used in in just a couple of blocks, thus *never* recommend addOverride, it is horrid.
For note, in MCP when developing I have it in my "MCP/src/minecraft/where-ever" and it is equivalent, it is part of my normal code tree.