Okay Mort, are you logged in as administrator on that pc?
And you can locate comdlg32.ocx in the System32 folder?
Did you try to manually register it again, and get a "successful" message?
(Btw, I also have Vista Home Edition, so it should work - let's see how we can persuade your pc

)
EDIT
One more thing, you might need to run the registration as Admin:
To open an elevated Command Prompt, click Start, click All Programs, click Accessories, right-click Command Prompt, and then click
Run as administrator.
Type:
regsvr32 %Systemroot%\System32\comdlg32.ocx
You should get the following message:
DllRegisterServer in C:\WINDOWS\System32\comdlg32.ocx succeeded.