It depends on exactly what you have now and exactly what you aim to achieve.
Since you give no specifics whatsoever, I cannot help you.
For instance: if you have a 7 speed cassette now ... you're going to have a hard time finding an old 7 speed road-crank.
Unless you are not talking about chinging your drivetrain but simply want to change to a dropbar ... then you can just fit any dropbar and roadstem easily.
You'd also have to change the brake controls and shifters, no?
Right. I was a bit drunk last night and overlooked this
Basicly, mr. reece, if you give us no specifics on what you have now and exactly what you aim for ... there's no telling what you need to do it as there are so many parts and so many combinations that will or will not fit.