The good news is that you might as well upgrade to 9 speed while you are at it. The STI levers are one of the most expensive components to buy so, if you've made the decision to change, you might as well go first class. Lots of folks are upgrading to 10-speed so there is a good amount of 9-speed stuff for sale.

If you decide to do that you will also need a 9-speed cassette and chain and, if you have a triple, probably a new 9-speed front derailleur. Don't forget to budget for new cables and housings and handlebar tape. The actual mechanical work isn't too difficult.