More that you probably ever wanted to know about Dura-Ace compatability can be found here;
http://www.sheldonbrown.com/dura-ace.html

Any Dura-ace derailler can be used with STI, potential limiting factor is the freewheel or casette. If the rear cluser is 7 or 8 speed, you should be able to use 8 speed STI levers (one missing ghost shift if you have 7-speed). If you have an early 6-speed casette or freewheel then you will need to upgrade to 7 or 8 speed to use STI.