what's the difference between these? are they made by different companies? What's linux to them? Do they look different? Do they have different apps? Are they more compatible with windows software and harware? Which is better? An answer to any of these questions will be welcome.
They have different desktop environments, which come with different programs. Ubuntu uses Gnome; Kubuntu uses KDE; Xubuntu uses XFCE. None is really better than the other, it's up to preference. XFCE uses less resources however if you're using an old rig.
There's also Edubuntu but nobody really wants that
1. Google image search each name and you'll see the difference. It is mostly the Window Manager (KDE, GNOME etc) that differs between them but each distribution has its own set of pre-installed applications that work with that WM. You can usually install a GNOME application on a KDE-based distribution (and vice versa) like Kubuntu although you may need to install GNOME first (you don't need to be running it, the libraries just need to be available).
2. Canonical Ltd. maintains and provides financial support for the distributions, including things developed by the community into newer versions.
3. Yes, quite a bit different. GNOME and Xfce are sort of similar but KDE is much more like Aero and full of eye candy.
4. Yes, but as stated above you can install apps designed for different Window Managers if you have the libraries for those WMs installed.
5. Should all be the same because at the core they are the same. However, if you need to run alot of Windows software you are better off just running Windows along side a Linux distribution in a dual-boot environment. Wine can run some Windows software in Linux but it's not meant to be a Windows replacement, it's more for those one or two programs that you can't find a Linux alternative for. It is better to run Linux software on Linux, and Windows software on Windows. As for hardware, the latest and greatest doesn't always work (particularly video cards) as the manufacturers are slower to release drivers for Linux but usually the hardware will work fine. Wireless network cards are an exception where you should make sure you've asked on some forums if a particular card will work. Wireless drivers all have to be reverse-engineered and rebuilt because many manufacturers don't release the source code for them nor do they even release closed-source drivers for Linux. Realtek-based cards (as in the actual chipset, not the brand on the sticker) generally work well but it is still case-by-case.
6. The beauty of Linux is that you can decide. One of the best things I've heard someone say when asked "which distro should I use?" is "pick a major distribution like *buntu, Fedora or openSUSE and just stick with it." Why? Because it's hard to learn your way around Linux if you jump from one distribution to another. It is like trying to learn how to use Windows but you use XP, 95, Vista and 2000 for a week each. You can of course try other ones but those three have large amounts of community support in their forums for help, which the smaller distributions may not.