The main thing you have to consider though is the rear dropout spacing. Modern hubs are spaced 130mm. Your old bike is most likely 126mm, so you'll have to set about respacing the rear dropouts. Fortunately Sheldon has this covered: http://www.sheldonbrown.com/frame-spacing.html
Switching to Ergo/STi is easy. All you need to do is replace the downtube shifters with a pair of these:
http://www.sjscycles.co.uk/product-Shimano-Shimano-Alloy-Braze-On-Down-Tube-Cable-Stops-with-Barrel-Adjusters-5511.htm
The main thing you have to consider though is the rear dropout spacing. Modern hubs are spaced 130mm. Your old bike is most likely 126mm, so you'll have to set about respacing the rear dropouts. Fortunately Sheldon has this covered:
http://www.sheldonbrown.com/frame-spacing.html