I developed carpal tunnel syndromes after a workout featuring push-ups and tricep dips off a step (I don't believe I was strong enough at the time for my anatomy to take the exercises, or maybe the problem was flexibility in the wrists?).
For a long time, I avoided tricep dips, and instead did lying tricep extentions (with barbells or dumbells). They are a good substitute, IMO.
I've also tried tricep dips with push-up handlebars, like Debbie's suggestion for using dumbbells.
After I did yoga for a while, and the stretches in P90X, I found I'm able to do tricep dips (and regular push-ups) with no wrist problems.