Returning to Apple after 30 years of PC - Need help

I’m thinking about buying a MAC but I have a few stupid questions I can’t seem to find easy answers to online. (Bot my first computer in 1983 - Apple 2+ but I switched to PC’s shortly after as that’s what was being used in the office world). I’m not looking to spend a lot of $, just a toy to see if really as good as the hype so I’ve been looking on eBay. Since I have no Apple OS, does apple charge for OS or OS upgrades? I assume they do, so I figure I should buy a system that comes with the original installation disks? I’m always reformatting my PC and having a set of Windows installation disks has been invaluable. If I buy a system with no disks and say version 10.4, how would I update it to 10.5 and what would it cost. If I then replaced the hard drive, how would I reinstall the OS on it without original disks?

Buy Leopard disk 10.5, for the upgrade and you can use that to install OSX on the new HDD as well.

Its always good to have OS disc. They need to be retail versions to install on most Macs not point update or machine only disc. Theres a big difference between PPC (older Macs) and Intel version disc. Also PPC machines and Intel Macs... Yes wail you where away Intel chips found there way into Macs.

I'm still having a hard time understanding. Maybe I asked to many questions at once. If I buy G5 iMac OS 10.5 with the original installation disks, can I use them to install a new hard drive?

Yes you can. It doesn't go looking for an installation /registration code like Windows does. The other alternative when replacing a hard drive is to "clone" the contents of the old drive over to the new drive. This results in an exact copy of your drive and the new drive can be used to boot your Mac. Once you know the clone drive is booting properly you could clone everything back to the original drive.

Wow are you in for a pleasant surprise. Windows 7 is like wading thru jello compared to my trusty old os 4.1.1. in a 3 Ghz G5. I use both daily and the pc makes me mad everytime I boot it. The pc is a new toshiba laptop 3.0 Ghz but getting around in 7 is not much different than doze 95. Too much mouse clicking and spurious layers to navigate.

Ron