Can I upgrade from MAC OS 10.4.11 to 10.5?

Hello, yes you can, assuming it meets these requirements, the $29 Snow Leopard/10.6 the cheapest...

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)

You have to call Apple & likely ask for a Product Specialist to get it, if they still have it!

Snow Leopard/10.6.x Requirements...

General requirements

* Mac computer with an Intel processor

* 1GB of memory (I say 2GB at least)

* 5GB of available disk space (I say 30GB at least)

* DVD drive for installation

* Some features require a compatible Internet service provider; fees may apply.

* Some features require Apple’s MobileMe service; fees and terms apply.

Which apps work with Mac OS X 10.6?...

http://snowleopard.wikidot.com/

It looks like they might still have it...

http://store.apple.com/us/product/MC573Z/A?fnode=MTY1NDAzOA

If it's a core Duo & not a Core2Duo, then it'll only run in 32 bit mode.

OK, great to hear. 🙂

I just talked to an Apple rep who said that I had to upgrade to Leopard first for $129

That's what they're supposed to say. 😉

Actually you can upgrade to Leopard first, but it is NOT essential to upgrading to Snow Leopard. You can skip Leopard entirely, unless you want to run something that is only Leopard compatible for awhile until you are up to speed for Snow Leopard or Lion.