No.
Mac OS X 10.5 is known as Leopard. The last available version of Leopard was 10.5.8.
eBay, because it is not the latest version of Mac OS X so is no longer available in shops or from Apple.
There is currently no version of Pivot for Mac OS X, free or otherwise. An alternative would be Stykz which is available for Mac OS X and is free. (See links below)
No. Ares Galaxy is only available for Windows.
Click on the Apple menu in the top left corner and select About This Mac. This will open a window which will give the version of Mac OS X you are running. From the Apple menu select Software Update... which will check if there are any updates available for the Mac.
Selecting Software Update from the Apple menu will automatically provide you with the latest version of Mac OS X available for your system. To move up from one version of Mac OS X to the next (for example from 10.4 to 10.5) you need to purchase a copy of the new version.
There is an older version of ClamXAV available (See links below) for Mac OS X 10.3 but as there are no viruses that attack Mac OS X anti virus software is superfluous.
Mac OS X Lion is version 10.7
The Mac's operating system was originally known as the System Software. It later became known as Mac OS followed by a version number - Mac OS 7, Mac OS 8 etc. The current 10th version is known as Mac OS X.
Mac OS X is one of the major releases of operating systems from Apple Inc. It features a low level Mach_kernel, underlying Unix OS, a 3D graphical user interface. Mac OS X can only be installed on computers made by Apple Inc. Recent versions of Mac OS X include: Mac OS X 10.3 Panther, Mac OS X 10.4 Tiger, Mac OS X 10.5 Leopard, Mac OS X 10.6 Snow Leopard. Starting in Mac OS 10.5 an automatic backup utility called Time Machine is available. The current version is Mac OS X 10.10 and an early release version of Mac OS X 10.11 is available to install.
You'll have to get a specific version available on the Mac OS X platform, unless the CD that came with the CD says it also works on OS X (such as Spore).
[A version of Mac OS X comes with every Mac. You must pay for any upgrades to a newer version] Not if you use torrents(: