Several members here have used the uninstaller described in the text below successfully. http://www.greenwood.iwarp.com/sgcomputer.html
Copied from link above:
Trouble installing or updating Zone Alarm in XP:
If you are having trouble updating or installing the Zone Alarm firewall, with error messages such as "Validation failed for..." any number of dlls, or that it can't shut down the True Vector Monitor, etc., here is the solution. First, if you were already using Zone Alarm, uninstall it. Second, there's a mess of files and folders you must delete. ZoneLabs gives lengthy instructions on how to do that, but to make it easy, I wrote a simple command file. Download and unzip the CMD file zfix.zip, then run it. It'll clean all traces of any old installation from your system, and you can now run a fresh installation with no problem.
To clarify why this happens, the explanation is simple. Uninstalling Zone Alarm in the normal fashion does not remove all the files and folders. When a new version of ZA is applied, XP prevents old files from being replaced by new files because of certificate verification mismatches. Thus, ALL old files have to be manually removed. This doesn't affect the computer or registry in any way. When the new ZA is installed, registry entries for the old installation are still valid as they simply point to newer versions of the exact same files in the exact same pathways.
WARNING: Zfix is an easily edited command file. If you downloaded it anywhere but here, you may want to verify it by right-clicking it, selecting the "Edit" option, and comparing it to this text:
rd /s /q C:\"Program Files"\"Zone Labs"
rd /s /q C:\WINDOWS\system32\zonelabs
del /q C:\WINDOWS\system32\Vsconfig.xml
del /q C:\WINDOWS\system32\Vsdata.dll
del /q C:\WINDOWS\system32\Vsdatant.dll
del /q C:\WINDOWS\system32\Vsinit.dll
del /q C:\WINDOWS\system32\Vsmonapi.dll
del /q C:\WINDOWS\system32\Vspubapi.dll
del /q C:\WINDOWS\system32\Vsregexp.dll
del /q C:\WINDOWS\system32\Vsutil.dll
del /q C:\WINDOWS\system32\Vswmi.dll
del /q C:\WINDOWS\system32\Vsxml.dll
del /q C:\WINDOWS\system32\zlcomm.dll
del /q C:\WINDOWS\system32\zlcommdb.dll
Any other text should be removed.