I currently have a bathtub that has never been plumbed for a shower. I have just opened the wall and see there is a vertical stub from the tub water supply. Is this a job I should get a real plumber to take care of? Should I open up all of the sheetrock from the tub supply to where the shower stub will come out of the wall? Thanks in advance...

A tub has a 1 1/2" drain and a shower requires a 2" drain. What is the rough in drain you have?

On top of Ballengerb1 advice, I would add mine too, if your question is only how to add a shower raiser,it will be easy to work to open up all of the sheetrock from the tub supply to where the shower drop ear elbow goes and it needs a support, also to use the Sharkbite drop ear elbow and Sharkbite coupling, see the images below, Thanks.

John

Good catch by John, I read this postwrong. If you have a tub and what to add a shower to the tub you will need the parts John listed PLUS a new tub valve diverter valve. You current mixing valve does not have a diverter and likely can't be converted. Replacing A Bath Tub Faucet (http://www.hammerzone.com/archives/bath/fixture_replace/faucets/tub1/moen_p1.htm)