www.parktool.com is the Park Tool website and has a great repair manual as part of the website.
I'd suggest doing the work yourself. There isn't anything that you can do installing shifters that would be devastating.
Worst case is you cut the cable too short ($5.00 for a new one) or cut the cable housing too short (again maybe $5.00 of material).
If you get hung up on anything, send me a PM and I'll talk you through it!
__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger