cdell

I have an older road bike and was considering buying some used Tiagra shifters from Craigslist. What else would I need to change on my bike to be able to utilize it. Currently it has a shimano exage rear and front Der. and a 6 speed cassette.

Would I just need a new 9 speed cassette? A new rear d with longer motion? Rebuild the wheel to accomodate the larger cassette?

I'm a noob so I really have no idea.

Al1943

This type of upgrade often costs more than it's worth.
Hopefully you're talking about new shifters, used shifters are a high risk purchase.
If you are committed you will need a cassette with the correct number of cogs to match the shifter (9-speed?). And you'll need a new chain of the correct width (9-speed?).
The rear wheel will have to be rebuilt or replaced with a wheel having a 130 mm dropout spacing Shimano compatible hub. The frame will have to be spread to fit the new hub, not a problem if the frame is steel.
The old derailleurs may or may not work. Chances are you'll need a later rear derailleur. You'll also need downtube cable bosses for the STI style cable housings. You'll need all new cables and housings, if the shifters are new out-of-the-box they should come with new cables and housings. And new bar tape, rim tape, etc.

Al

AndrewP

Needs a new rear wheel because you will need a freehub + cassette instead of a freewheel. This is a real upgrade in terms of rear axle durability. If you like the fit and handling of your bike it is worth it, but it will approach the cost of a new bike.