Hey, so I want to install a Linux OS on my machine that is running windows 7 beta so I can switch between the two.
I don't know much at all about Linux, so I'm wondering which Linux distro I should be looking at? I've been looking over Fedora, Debian and Ubuntu, and it seems, from what I've been reading, that ubuntu is the easiest to use. However, I'm more interested in the best OS, not which one is the easiest to use.
BTW, ill probably just be using the Linux OS for messing around with programs. At least for now.
There is no best. It's a matter of personal preference, and we can't really tell which you will like. The best thing to do is pick one, make sure it works with your hardware and then stick with it until you know the OS well. Chopping and changing distributions like they go out of fashion will make it harder to learn the core skills common to most, as you'll spend so much time getting used to all the aesthetic changes.
Note: I have about 10 distributions and don't know any of them well.
2.6.x will be the kernel version; keep away from Debian untill you have some experience of Linux, it isn't intended for Linux Noob's; easiest way to get started is to get an Ubuntu live CD (which is friendly re-work of Debian) and give it a try, the live CD will allow you to give it a try without having to install anything and will give you a good idea of how compatable your hardware is, if you like it, you can install from the live CD.
You can also try installing via Wubi. This allows you to install it "within" Windows like a program and it will show up in Add/Remove Programs as well. It's put on a virtual hard drive and is a complete and usable installation unlike a Live CD. It's not dead slow like a Live CD either It's not as stable or bug-free as a "proper" Ubuntu installation though, and because it's installed on the same NTFS filesystem that Windows uses, it is subject to fragmentation slowdowns. The advantage is that you can try it as though you were running a proper installation and remove it easily if you want a change.
Note that only Ubuntu and its derivatives support Wubi. This includes offshoots like Linux Mint as well.
Desktop environments and window managers define the "look and feel" of the OS, as well as providing the libraries for developing and running applications on them. They are a layer between the user and the X Window System which is what controls the GUI at a lower level (it's basically a protocol). X does not control the look of the OS itself.
GNOME, KDE, xfce and a few others are the window managers which control what you actually see and interact with. They all have a different default look and set of applications, but can all be customised as well. Most distributions will make noticeable aesthetic changes to appear unique. Googling KDE, GNOME etc will give you more info as well as screenshots to compare them.
KDE is usually considered the "eye candy" window manager, GNOME is the most widely used (although by no means objectively the best), and xfce is targeted towards lower system resource usage and looks somewhat like GNOME. You can have any number of window managers installed at any time, but only one can be running at once (I think), at least in a single-PC configuration.
It will slow your PC down about as much as Aero slows Windows down compared to running a complete command-line interface - Not enough to justify the ugly black and grey screen of the CLI unless you find it more efficient than a GUI
Before choosing a Linux distribution you should ask yourself what you need to do with the system. When you know this it get's easier to choose. And I would recommend that you make YouTube searches on different distributions to get a feel of it.