Installing a showerhead in a bathtub that doesn't have one is a big job. An easier solution is a flex-line shower unit. It installs quickly, and its removable showerhead is a handy feature.
The surrounding walls should be covered with tile or other water-resistant material. If you have a claw-foot tub that does not abut the walls, purchase a circular shower curtain.
About an hour for most units
Drill with masonry bit, screwdriver, hammer, groove-joint pliers or pipe wrench
Drilling holes in tile, assembling parts
No need to shut off the water; place a towel in the bottom of the tub to catch any parts
Flex-line shower unit, pipe tape, plastic anchors