I used CE-star that is particular for Palm. Works very well. You need to go here to download the Palm treo specific version of the CE-star.
http://mobem.com/products/cestarwm5palm.php
It says it was for WM5, but it worked for my Treo Pro (CDMA, Sprint).
There was a small kink though. After the initial installation, I couldn't use "option+space" to switch between English and Chinese. I contacted their tech support guy, they ask me to run a grabtest.exe in my Palm and send them a file (generated by grabtest.exe) containing some setup info. They then sent me back a modified "cstar.set" to be placed in the installation folder (there was a cstar.set in the installation folder already, you need to replace the one in the folder with the one they send you). After that, I reinstalled the CE-STAR, everything worked perfectly. I could now read email, SMS, website in Chinese and enter Chinese as well.
If you want to call their tech support, be ware that they are in Beijing, China. They are 12 hours ahead of the US Eastern time. If you call during the day in the US, there would be nobody there. Need to call after 8PM EST.