prnadmin.dll hp print processor

I am having problems installing HP printers on remote PC's using
prnadmin.dll (http://support.microsoft.com/kb/321025/). These are all
Windows XP Pro PC's. One example of a problem printer is a LaserJet
1350. I found that the pc I was trying to install to did not have the
HPZPPxy print processor, Which no new Pc would, the install will fail.
I can copy HPZPPxy.dll to the print processor directory and update the
registry then reboot for the OS to reconize the new print processor.
Then Installing with prnadmin.dll works flawlessly.
This is also the case when trying to install a LaserJet 4200 both use
the HPZPPxy print
processor. I imagine the same is true with any printer install that
requires a print
processor other than the one provide by Win XP.
If you install a printer with add printers wizard the print processor
is installed
without having to reboot. So I don't understand why one is needed in
this case or more I don't understand why the print processor is not
installed from the inf. Does anyone know how to make this work with out
a reboot.