Vista will not be like Linux in any way though I hear they may try to implement a basic security feature found on *nix OS's, the super-user.
Having said that if your really interested in Linux then try out a few Live Cd's. They allow you to run Linux from a CD without having to install Linux to your drive. Live CD's have many many uses but it's a great way to get yourself familiar without having to commit to installing it.
Have a look at this thread I put together in the Linux Forum. It has allot of great links to help get you familiar with Linux and where to get distros, both Live CD's and full installation distros.
Tech Forums Linux Links
From a Live Cd standpoint most people go for Knoppix, Mandrake Move or Slax. Any one would be a good choice.
As for full blown install distros for a beginner I would recommend either Mandriva (formerly Mandrake) or Suse 9.3 Pro. Read, read and read as much as you can about Linux so that you can familiarize yourself. It's very different from Windows. Especially read up about the distro you plan on using. Good luck.