Hey, i have 10.5.2 and changed the systemversion.plist and iwork 09 works great.
To do so, do the following:
Go to System/Library/CoreServices, then you will see SystemVersion.plist, copy it and paste it on your desktop.
I suggest you also make a backup just to be sure....can't hurt.
Then open the plist from your desktop and where the string is that has your system version--- 10.5.2 for example, change it to 10.5.6.
The version should appear twice in the plist, so change both.
Then save the plist and paste/replace it over the old systemversion.plist, put in your password, and check your "about this mac" to verify.
Then install and you'll be fine!
Worked 100% for me!
Posted is a pic of the plist, also, there is an automatic installer posted somewhere-- search for JSN1 System Version Changer--it does not go up to 10.5.6 but you could go to 10.5.3 then manually change it...that is my process because previous applications needed 10.5.3
Hope this helps! Worked for me, good luck!
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