If you are looking for the most similar intereface, I believe that would be any distribution based on KDE, like Kubuntu, SUSE, Mandriva, Knoppix, (Im not a Linux expert tho I'm pretty sure I got those right :) )
First off, I Highly recommend if economically possible to purchase Linux PRE-Installed, especially on Laptops!. Although you can also try a Live CD to test a version before installing it, as mentioned above, nearly every distribution has them.
I switched from Windows to Linux last summer, and I choose Ubuntu. And it seems to be Very very fast on my machine. It also seem plug and play, except for some printers. (Lexmark for me wasn't, but HP was plug and play) Internet connectivity is much easier than windows!
I also recommend Ubuntu because of the support , ubuntuforums.org Is Very active forum, questions answered Probably the best support of any distribution. I also felt confident as it was selected by Dell, a major distributor, and basically the only one in the US to support Linux for home users. www.dell.com/open
While its not exactly like Windows, I found it extremely easy, actually easier to use, and the layout is not that different anyways. Also you can get a free CD shipped to you, through https://shipit.ubuntu.com/
For other distributions check out http://distrowatch.com Very informative on almost every version.
Personally, If you don't choose Ubuntu, I would stick to one of the other major versions such as SUSE, or Mandriva, which are likely to have more support, which is essential!