I was able to get the Trial version of CS4 to install but then I had problems and uninstalled it the second day. More on this problem in another post.
Ever since this uninstall the trial version refuses to install again.
One of two things happen:
1) The trial install completes but then displays an error saying the install failed "one or more components failed to install" -but gives no details. If I try to launch the program anyway it asks for a serial number even though it was installed as a trial.
2) The trial install completes but asks for a serial number.
The trial spent a total of about 30 HOURS on my computer so it's not possible that it ran over the trial period.
There have been no previous versions of Premiere (trial or full) ever installed on this computer.