Q: Can I upgrade my G4 1.33GHZ to Leopard?

Hi & a warm welcome to the forums!

Yes you can upgrade, Leopard requirements/10.5.x...

    *  Mac computer with an Intel, PowerPC G5, or PowerPC G4 (867MHz or faster) processor

minimum system requirements

    * 512MB of memory (I say 1.5GB for PPC at least, 2-3GB minimum for IntelMacs)

    * DVD drive for installation

    * 9GB of available disk space (I say 30GB at least)

Trouble is Apple no longer sells it, check eBay & such for the Retail version, not the Gray Discs...

http://www.ebay.com/sch/i.html?_nkw=mac+os+x+leopard+retail+10.5

List of Applications Not Compatible with Leopard...

http://guides.macrumors.com/List:Applications_Not_Compatible_with_Leopard

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  Leopard 10.5.6 install DVD (single user)

MB022Z/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

The DVD should look like this

Caution - Leopard does not support classic mode. So, if you currently open OS 9 apps in classic mode, you won't be able to do this if you upgrade to Leopard.

 Cheers, Tom

You can upgrade to Leopard.  But you will lose access to Classic.  If you ever see your Apple menu turn rainbow colored, then you need to upgrade that application before you can use Leopard with that application.  Upgrading may help on some applications, but your processor is too slow for some website animations.

By losing Classic, that means any program that changes the Apple menu to a rainbow color will no longer be able to operate until upgraded to not need Classic.  Of course you should make sure all your programs are known to work with Leopard as well as any printers, scanners, etc...