Q: can I buy an upgrade for Power PC from 10.4 to 10.5 or 10.6?

That computer can't run an OS newer than 10.5.8.

(65529)

Greetings Terry,

10.5 would be the highest OS you can upgrade to: http://support.apple.com/kb/HT3759

Make sure you have a backup of your data before you install a new OS: http://support.apple.com/kb/ht1553

Make sure all applications you use are compatible with that OS before you upgrade.

Cheers.

You'll need a 10.5 Leopard retail installer disc.

You can ask Apple Phone Sales if they still have any left; expect to pay about $130.

Otherwise, it's Amazon MP or the 'other place', but expect to pay considerably more; they seem to be in demand at the moment.

Be sure it's the right disc -

That's the box, but the disc is the same logo.

Some info from TexasMacMan (amended by me for latest part nos.)

Mac OS X 10.5 Leopard installation system requirements

http://support.apple.com/kb/TA24950

Leopard is no longer available at the Apple Store but may be available by calling Apple Phone Sales @ 1-800-MY-APPLE (1-800-692-7753).

If you can't obtain a retail install DVD from Apple, look on eBay or Google the installer part numbers to possibly find at an on-line store. Here's what to look for:

MB427Z/A  Leopard 10.5.1 install DVD

MB576Z/A  Leopard 10.5.4 install DVD

MB021Z/A , MC094Z/A  Leopard 10.5.6 install DVD (single user)

MB022Z/A , MC095Z/A Leopard 10.5.6 install DVD (5-user family pack)

Installing Mac OS X 10.5 Leopard

http://support.apple.com/kb/HT1544

Mac OS X 10.5 Leopard Installation and Setup Guide

http://manuals.info.apple.com/en/leopard_install-setup.pdf

After you install the base 10.5, download & install the 10.5.8 combo update at http://support.apple.com/downloads/Mac_OS_X_10_5_8_Combo_Update

Note: 10.5 will not run Classic.  keep a copy of 10.4.11 or earlier on a second hard drive if you are using Classic.