I would agree with everything PaulinVictoria said. It mirrors my own experience almost to a T.
I won't repeat everything he said, but I would reinterate a couple of high points...
1) You don't need to remove Vista. As a standard part of the install, Ubuntu (Ubuntu is the 'name' of the current Linux version) will ask you if you want to create a seperate section of your harddrive for Linux. If you choose yes, then you will be prompted to decide how much space to give each operating system. I gave my windows side only about 1/6th of my 80 gig harddrive.. and it's more than enough. By doing this, you can always choose to boot into windows as if you had never installed Linux, so really, you risk nothing. And every once in a while, you might want to remind yourself why you'll never go back to Microsoft again
2) Opensource software is awesome! Yes, it has a few bugs. But there are literally thousands of people far smarter than you or I out there working on them right now. And in the next couple of days, an update will come out to fix things. It's amazing how quickly the Linux/Ubuntu world moves. And unlike Mac, they don't fix things by simply limiting access to certain software (how's that flash working, IPad users?). They just fix it.
3) Not everything works with Ubuntu. The only thing I can't do so far with Ubuntu is watch netflicks movies on my computer. I use the windows side for that. Everything else (word processing/image manipulation/games/internet browsing/etc) I use the linux side for. So, thus far, Netflicks movies are the only thing I've found that Ubuntu won't do. I'm sure there's something else, though. I just haven't found it.
4) Ubuntu is FREE. I haven't paid for software in about 2 years. Not because I pirate it, but because when you use Ubuntu, you don't have to. I do, from time to time, send $5 or $10 to a developer if I find a particularly cool chunk of software. But then, I know it's actually going to the guy who coded it rather than the billionare CEO and his company. It's nice to know your money goes where it should.
Guess I am going to get long-winded. The bottom line is that you have no risk here... give it a whirl, and if you hate it, you aren't committed to anything.
Oh, as a final note... when I turn on my netbook using windows XP, it takes about 2 minutes to fully 'boot'. When I turn it on with Ubuntu, it takes about 45 seconds. For what it's worth.