I can't change administrator password on G5 PPC OS X 10.5.8
If you're referring to this thread, then from looking at your screen shot it appears that you didn't enter exactly what was specified. For example, there was the command mount -uw / but you didn't put the space between the command switches and the slash. Since that didn't execute the mount that you wanted, I'm not surprised the rest of it didn't work :-)

As a side note, though Apple HFS+ installations tend to be case insensitive, it is always possible that case sensitivity is enabled on the computer. As such, you entered the rm .Applesetupdone line incorrectly since it should have been .AppleSetupDone.

You'll probably have improved luck with the mount statement, but when working with the UNIX shell you should always be case sensitive and careful with spaces, dashes, quotes, etc. since UNIX traditionally is VERY sensitive to these things and the wrong keystroke can render the OS installation non-bootable.