It's something I'm in the process of doing, so I'm speaking more from hope than experience!
Broadly speaking, you'll need
cable stops which fit in place of your down tube shifters;
a set of cables (dimensions are different to regular cables) and, of course,
a pair of combined brake and shift levers (scroll down).
You will need to choose between Campagnolo (Ergo-power) and Shimano(STi and Shimano compatible systems from SRAM and Microshift): it is possible, in certain circumstances, to "mix & match" but it isn't something for beginners.
You should also be aware that mixing "speeds" (ie number of gears) can cause complications because the gears can have different spacing and consequently the shifters will pull different amounts of cable.
As far as I know, 5 speed gears pre-date "brifters" and although you might be able to fit a 7 speed freewheel, 7 speed brifters aren't common.
What is the
OLD of your frame?
NB The links are just examples, the first thing that came up on a search and won't necessarily work together.