Q: I use OSX 10.8.2 and tried installing my iWork '08 disk.  Result? The software is no longer compatible. Is this correct?

Unfortunatly yes.  You would need to upgrade to '09 for iWork or if you only use one or two of the apps at least you can only purchase what you need. i.e. you can buy just Pages and not the other two.

You buy it through the application.  It is really simple!  And, you can save it to a disk, but if something bad happens all youneed to do is log in again and re-download what you purchased!  After that you get Delta updates.  I remember back in engineering class that Delta ment "change", so I think to keep things small they do not update with the whole program, but rather with just the changes to what you have.

I still haven't figured this out!

I have the disk for '08 -- should I not bother to load it? What about my key for the upgrade to '09?

According to the Roaring Apps Site, iWork 08 should work:

http://roaringapps.com/apps:table/tags/_i/index_tags/_i/p/2

I use OSX 10.8.2 and tried inatalling my iWork '08 disk. Result: iWork Software runs on 10.8.2, i'm able to open documents created by pages/numbers/keynote on OS 10.5.8 BUT: all characters are invisible. After the text is marked e.g. by "cmd+A" all characters are visible. A change of the charavters's colour does not solve the problem.

Does anybody have an idea what's the problem and how to solve it?

Do a backup, using either Time Machine or a cloning program, to ensure files/data can be recovered. Two backups are better than one.

Try a restart.

Run Disk Utility/Repair Permissions. Run until it reports no errors. If there is a recurring error, see the article on what permission errors can be ignored.

Disk Utility                                                       

Disk Utility Repair Permissions You Can Safely Ignore

Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.

Isolating an issue by using another user account

If the problem is still there, try booting into the Safe Mode.  Shut down the computer and then power it back up. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart. For each disable/delete, you will need to restart if you don't do them all at once.

Safe Mode

Safe Mode - About

General information.

Isolating issues in Mac OS X

Troubleshooting Permission Issues

Step by Step to Fix Your Mac

Upgrade Nightmares  

Try posting on the iWork communities.