1) You can either order the disks or download them, or pick them up as an add-on to a book. For example, the book "Linux for Dummies" comes with a set of disks, Red Hat last time I checked. The Linux Bible comes with both Red Hat and the "live" distribution Knoppix.
To download a distro, you can either use Bittorrent or a straightforward download. ISO mirrors include Linuxquestions.org and sorceforge.net.
Technically speaking you aren't "buying" a Linux licence, but rather either support or the cost of burning and mailing the physical disks.
2) Version... There's two definitions I think you could be driving at: distributions, and the distributions' versions. I found Mandrake (now Mandriva) quite easy to use, it automatically sectored my hard drive and set up the boot as a Dual Boot, leaving me with the option of booting into Linux or into Windows. Handy at tax time, as nobody has a Linux tax preparation program.
Another newbie-friendly distribution is Linspire, and there are PLENTY of others. If you want to start a fight on a Linux forum, just claim that such-and-such a distribution is The Best There Ever Was. ^_^
I recommend trying first a Live Distribution, like Knoppix. They fit on a single CD, and rather than installing on your hard drive, run off your CD drive. When you remove the disk from your CD drive, Presto! the next time you boot your computer, you have a Windows machine again. You don't need to (although you CAN) install the Live Distro on your hard drive at all. That way you can "test-drive" your hardware without worrying about mucking up your Windows setup.
3) Number of disks: your milage will vary depending on which distribution, and which version of which distribution, you choose. Live distros by definition fit on a single CD-RW. Mandrake 10.1 Discovery fits on 3 disks, which includes enough software choices to turn your humble home computer into a full-fledged Internet, e-mail and file server with office productivity software and games as well, but will only install those you need for your particular situation (i.e., if you just want to surf the net it'll ignore the various types of server software).
4) How much resources: If it's got at least 128 MB of RAM, it should have enough to run any type of Linux install, typically with the KDE or Gnome Graphical User Interface (GUI). For older machines with 64-MB or less, you may want one of the less resource-hogging GUI's like IceWM or XFCE4.
I've seen people claim to use 386's and 486's as firewalls, printer servers, etc., using distros like damnsmalllinux. I strongly suspect they're running it off the command line, rather than trying to use a GUI.
The trick is: YOU DO NOT *NEED* TO INSTALL a graphical user interface. You can run the system from the shell command line.
5) Time to surfing the net: With Knoppix, the time it takes to boot up, plus the time it takes to entering in the info to connect to your ISP. With a full installation, possibly a couple of hours until it installs all the software on your system.
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I strongly recommend that if you have ANY problems, you surf over to Linuxquestions.org and do a little bit of searching. You'll probably find that someone had a similar problem to yours, and got a solution.
Good luck, and enjoy Linux!