Do not install Ubuntu. Do not install anything -- yet. Unfortunately, installing any OS involves repartitioning the hard drive. This can be very tricky and can easily lead to losing everything on it. So don't.
There is something called the LiveCD which you boot from CD or some other removable drive, and it loads the whole OS in memory -- it does NOT write to disk unless TOLD to so you will NOT be compromising your computer with it. Ubuntu has had several. Generally they are integrated with the install disk these days, so you can use them to surf the net. Frankly, Ubuntu's LiveCDs are not among my favorites.
They are slower than installed OS-es. It takes longer to access a CD drive than it does but your average LiveCD provides a Windowing operating system, a web browser, a word processor and text editor. Unless your liveCD is Ubuntu it also includes the GCC compiler collection, incidently, and I have done coding on Knoppix.
Anyhow here is a list:
http://www.frozentech.com/content/livecd.php
You get started by either downloading and burning an iso file using Nero or some other program which is a good use for part of your 10G or ordering one usually for about 10 bucks from one of several vendors you can learn about by going to http://www.distrowatch.com
My favorites are:
Knoppix: an engineering distro which nevertheless has a simple KDE desktop like Kubuntu. If you run into trouble you can ask your Kubuntu using friends and they will steer you the right way whether they know the answer or not. An engineering distro means in this case, not so much it's complicated but that it is precise and correct. It tends to run straight out of the box. Because of a trademark dispute they have a program called Iceweasel. You will see an icon at the bottom of a little white creature with its arms around a green globe. The dispute was between the Debian Foundation and the Mozilla Foundation. The current situation is that Debian may include Firefox but they can't use any trademarked or copyrighted material such as the firefox name or icons. Canonical, who does Ubuntu, has made a separate deal with the foundation but the Knoppix people can't afford to. For word processing I suggest AbiWord.
dyne:bolic is a very strange but very good LiveCD geared towards media production. You boot it up and it has just about everything you need for mixing tapes or editing videos. There is office software and web browsers -- you call up the menu by right-clicking anywhere on the desktop. The project leader is an Italian Rastafarian who lives in Amsterdam (which explains the strange smells). As a liveCD it's great, but it offers an installation option called "nesting". Don't. Think of it as a product of those pungent smells
Damn Small Linux (familiarly, DSL) is the smallest. 50 megs. The default desktop is either JWM or fluxbox, which is actually favored by some engineers because it leaves so much memory for other programs. The default browser is dillo, which is useful but firefox -- meaning firefox itself -- is available on it.
PCLinuxOS and Mepis are two more which are worth commenting on. They both try with not total but reasonable success to make the Linux experience as Windows like as possible. They are both fun, useful desktops regardless.
My current favorites are the XO Laptop livecd which gives your computer the open source Sugar interface of OLPC and Slax, which is a derivative of Slackware, but just fun. Also on that list, by the way, is Freesbie, which is not a Linux LiveCD. It is a FreeBSD UNIX liveCD. And it will give you a taste of Unix with as little hassle as you can get from the Linux LiveCDs. If you want to try out Linux, I recommend livecds. Ubuntu has one too. If you want to go on to install something, Ubuntu is a good choice, especially with wubi installer which you can get at http://www.wubi-installer.org, but if you just want to try out Linux, don't install anything yet. I gave you a list of livecds -- or links to a page of links to livecds. Try out them first, and while it will be slower than the real thing it will save you so much hassle...