I'm trying to create a new dimension and the only problem i'm having is with the grass. I can't get the side and top textures to change according to the biome if someone can help me it would be much appreciated.

It's not exactly the easiest thing to do, depends on how far into modding you've gone, but the vanilla grass block has hard coded checks to make sure that the default named textures are the ones being used, so if you try to create a new grass block and try to specify your own textures, it won't render the same way as the grass block.  You need to make your new grass be rendered by custom rendering class.  So basically I went into the RenderBlocks class, copied all the code relevant to rendering the grass block, put them into my own custom rendering class and removed the vanilla checks that look for the default textures.

 

It depends how far along and how much you know, when I first wanted to do this I was too much of a newb but after modding for awhile I figured it out.  If you need help let me know.