error_log:
[2012-05-23 13:18:21,223] ERROR com.google.gerrit.common.ChangeHookRunner :  
Error running hook C:\Projects\gerrit\hooks\change-restored
java.io.IOException: Cannot run  
program "C:\Projects\gerrit\hooks\change-restored" (in  
directory "C:\Projects\gerrit\git\Project.git"): CreateProcess  
error=193, %1 is not a valid Win32 application
        at java.lang.ProcessBuilder.start(Unknown Source)
        at  
com.google.gerrit.common.ChangeHookRunner$HookTask.run(ChangeHookRunner.jav a:499)
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
        at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
        at java.util.concurrent.FutureTask.run(Unknown Source)
        at  
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access $201(Unknown  
Source)
        at  
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Un known  
Source)
        at com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:333)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: CreateProcess error=193, %1 is not a valid  
Win32 application
        at java.lang.ProcessImpl.create(Native Method)
        at java.lang.ProcessImpl.<init>(Unknown Source)
        at java.lang.ProcessImpl.start(Unknown Source)
        ... 11 more

Can this be worked around by adding an extension then changing  
gerrit.config's [hooks] section to point to the new name?

It can. I use a batch file and it works.

Like Tortoise, it should probably look for *.exe, *.bat, *.cmd.