Yes, however, read about the pitfalls below.
Mac OS X 10.5 was release October 26, 2007. Its 10.5.8 update is the newest operating system available for PowerPC Macs that meet its requirements. It is available occasionally by calling Apple online store's phone number, even though the website does not show it. Many want to upgrade to Leopard because of i-Devices (iPhone, iPad, iPod) bought saying iTunes 10 or later is recommended. To check if that really is required, look at the i-Device requirements section of this tip
If your Mac is Intel, and running 10.4.11 or earlier, and meets the hardware requirements of 10.6, a less expensive upgrade solution is to upgrade to 10.6 directly. No need to upgrade to 10.5 unless your software won't run in 10.6.
Software listed for Intel Mac and PowerPC Macs can run on 10.5 for the platform indicated in the link. For Leopard you need
867 Mhz on a single processor or faster (1 Ghz and higher are faster).
256 MB of RAM (preferably 512MB of more based on arbitrary experience).
9 GB of hard disk space (arbitrary experience adds another 15%) free.
Macs newer than August 28, 2009 can't run Leopard, and require a minimum of Snow Leopard.
Dual booting Mac OS 9 and Mac OS X 10.5, check this tip:https://discussions.apple.com/docs/DOC-1757
Classic is not compatible with 10.5. 10.4.11 on a PowerPC Mac or earlier is needed for Classic.
Mac OS X 10.5 is the earliest version of Mac OS X that will run iTunes 10. This is necessary for numerous i-Devices (iPad, iPhone, and iPods). To find out which require it, see this article
http://en.wikipedia.org/wiki/ITunes_version_history
Should you require only iTunes 9, and are running a minimum of 10.4, backup your data at least twice, check in Apple menu -> About This Mac if you have a G3, G4, G5 (which is PowerPC), or Intel Core (which is Intel) make sure you are running 10.4.11 PowerPC or 10.4.11 Intel (depending on the aforementioned processors), and download iTunes 9.2.1. The only reason you should upgrade to 10.5 is if some other software is required.
Boot Camp is only available on Intel Macs with 10.5 and higher.
Time Machine backup software first appeared in 10.5
You have several options of installation which are explained here: https://discussions.apple.com/docs/DOC-2209
All of which I recommend you backup your data at least twice before upgrading, and have sufficient disk space to install, and all your third party applications and drivers are known to be Leopard compatible, and after backing up your data you dismount and disconnect all but Apple keyboard and mouse and if there is an external display, that too. And just before you install repair permissions.
If any of the above terms confuse you, ask on the Discussions board what they mean, and one of the people who knows will gladly assist you.
You must use the installer disc that looks like 
*, and does not say Upgrade, Dropin, or OEM, if you choose to upgrade to Leopard.
Message was edited by: a brody
