Help! Error creating folders, when installing 5.5 in OSX 10.3 for first time

I am trying to install Photoshop from scratch on a G5; I have an upgrade path, but it starts with 5.5. When I try to install 5.5, I enter the serial number, move to the next screen and it starts to install, only to have the messege "Error creating folder" come up. Have tried several of the 7 serial numbers we use at this location, to no avail. Anybody have an answer? I'm really stumped!

You don't need to install any early versions.

when you install 7 you need to enter the old number it looks like this: XXX000X0000000-000 (letters are X nunbers are 0 )

then the new number it looks like this:
0000-0000-0000-0000-0000-0000