Some things to note from a ~3 year Ubuntu/Linux user:
- This is not windows. It will not operate, function, or act anything like windows.
- The command line is useful and extremely powerful, but pretty much never needed for daily use. That seems to be a common misconception.
- As pointed out above; DVD/MP3/etc. playback is not supported out of the box. This is due to copyright reasons. It's a very simple and quick download to include it all of however. Microsofts .NET Framework and Silverlight technology is currently being ported over to Linux systems (Mono and Moonlight) respectively). Both of those projects are actually supported by Microsoft.
- Gaming is not even close to being as good as Vista (for obvious reasons), but the amount of windows programs Wine runs will amaze you. I regularly play WoW, Rome: Total War, and Neverwinter Night 2 on my machine.
- The amount of customization avaible will blow you away.
- Installing/Updating every application on your computer can be done by the Update Manager. Very simple and easy. No hunting down new versions on the internet and re-installing them.
You should be fine with hardware support. When I first started playing around with Ubuntu 3 years ago it was an issue, but the ONLY issue I ever see now is wireless cards and bluetooth devices. Both of which have extensive troubleshooting guides that will get them running for you. Your nVidia card will use the basic open source driver. To use nVidia's driver (and activate all of the cards potential) you just go to System --> Administration --> Hardware Drivers then "activate" the nVidia driver. It'll automatically download and install the latest driver. They do it this way for people who only want "free and open-source" on their machines. My eVGA 9800 GT works like a pro.
I much prefer Ubuntu over Vista. Vista is pretty much "babies first OS" and most people just don't bother to learn more about their system to run anything more complex than Vista. You can get a completely customized system catered to you, but it'll take some time and learning. I'll be happy to point you in the right directions if you want to give Ubuntu a try.