Well in that case I'd recommend that you reinstall your English-to-Chinese dictionary database. Here's how:
1) Go into your Palm Desktop user folder (c:\program files\palm\(your useranme)\) and delete all of the files inside of the "Install", "CardInst", "QuickInstall", and "Packages" subfolders. This will clean out any files that may be jamming up the install process and preventing the E-C database from installing.
2) Download the "Oxford E&C Dictionary Only" "Manual Install" version of PlecoDict, pdox102.zip, from
http://www.pleco.com/palmdownload.html.
3) Follow the instructions in the manual (
http://www.pleco.com/dictmanual.html) to perform a manual installation of PlecoDict to your Zire. However, when you get to the point where you're supposed to select databases for installation, select only "Oxford E-C.pdb" from the Dictionaries folder. And don't put it in the Expansion Card section of QuickInstall, since it sounds from your e-mail like you don't have a memory expansion card for your Zire.
4) After the install finishes, run PlecoDict again and you should have a working E-C dictionary.