Subfloor Question

Well, I Have Decided To Go With A 54"tub In The Bathroom, I Have The Tile Cleared Up From The Floor And The Walls Removed And Cleaned Up, When I Put The Subfloor Down Should I Also Put It Under The Tub Before I Install It? And Which Is Better Hardibacker Or The Regular Concreet Board?

You don't need the cbu under the tub. CBU is NOT structural, and typically you only need 1/4" stuff for the floor. Before you put tile down, double check the structural suitability for use with tile. Suggest you go over to www.johnbridge.com they are tile experts. Very useful help and info.

you should have a min. of 1 1/4" of wood under the tub. then lay cbu down up to the tub to "lock it" in place.