Thanks again Richard!
It looks like you are in luck and both Macs can be upgraded to the latest version, OS X 10.8 Mountain Lion.
First you must upgrade to 10.6 and going from OS X 10.5.x to OS X 10.6.x is a paid upgrade.
For a limited time, it may be available via the Apple Online store in the US:http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard
It is no longer officially sold in most stores and if you can't readily find it most customers have been able to get it via telephone.
Call 1-800-MY-APPLE (1-800-692-7753) and tell them you want the Snow Leopard upgrade which they can send on CD for around $20 USD shipped.
Once you have the disc, the upgrade process is fairly simple. After the install, keep running System Preferences > Software Update until no more updates are offered.
Once you have 10.6.8 installed, you will then be able to upgrade to the latest release of OS X (10.8 Mountain Lion) via the Mac Store. Sadly, you must have 10.6.8 installed first to upgrade further.If you continue to have questions on this topic, just reply back to this discussion. I will be more than happy to work with you further. Hopefully, this info will answer your question
. If so please, please remember that when you are asked to give a rating, you are rating my personal service only and not this website itself or your issue.
Thanks and good luck,