I am an aged retired professor of EE, who started using Linux about a year and a half ago. In my considered opinion the best Linux system for a rank newbie, in Linux, to start is to download Knoppix, any version later than 3.0 will 'find' all the hardware on most, if not all, PC systems (yes! no downloading drivers). Put Knoppix on your hard drive, leaving windoze there, use either GRUB or LILO as a boot-operating-system selector (search the Internet using how-to 'task', but be careful not all Internet articles are cool). You are smart to keep your windoze system running until you can safely shift completely to Linux. Use the Internet for any questions (feel free to ask questions of any tested Linux user). A single source of information which helped get me started was Carla Schroder's 'LINUX Cookbook', O'Reilly, isbn: 0-596-00640-3, which may be a bit dated by now, but a very good source of Linux 'how-to' information. (There are several articles on the Internet by this author which you will find very helpful, also O'Reilly books has a cool on-line service.) I started with Knoppix went to Slackware, then to Mandrake, Mepis, then Ubuntu, (to name only a few) finally shifted to just plain good old Debain Linux. Debian, in my considered opinion is the very best of all Linux operating systems which I have tried. Its 'apt-get' and "aptitude" operated from the console (command line) give you the best selection of free software available for Linux operating systems. This software is free for the download, and these two commands, see'~$ man', will connect, using sources.list (/etc/apt/sources.list), then download any or all software for you. Linux operating systems always have manual (~$ man 'command-name') avaiable to help us newbies learn to speak Linux. (There are also 'alien' to convert pkg.tgz to pkg.deb, and '~# dpkg -i pkg.deb' to install non-debian software packages on Debian.) (note: 'aptitude' and 'apt-get' both use 'dpkg' to complete their work, I am told.) Slackware is my, kind of, second choice Linux operating system, however, it tends to maintain some of the older Unix tradition. I have 'tailored' my Debian Linux systems to suite my needs, keeping my home directory separate (on a not-to-be formatted partition but use as
/home/kb6vdo, for example) so that all my favorite settings are not disturbed when the urge strikes me to add a later or different version of Debian, or any other, Linux operating system to my collection of running operating systems on this box. Mix other Linux distros with care! If worried use a new alias user name instead of your choice a redo all your gui settings.
Knoppix, Ubuntu, and Mepis, when I used them, were all three based on Debian Linux, but tend to modify the source code to suite their own needs, not mine. This source code change makes distribution upgrades dangerous for newbie linux folks.
Linux is wonderful, it has more and better free scientific software as well as highly specialized free publishing software avaialble, I dare say, than you can even purchase for windoze. Linux is virtually unlimited in its scope of useful possiblities; it is, practically, the modern day Unix which was and is designed for both academic and research use. As far as I know the only area where windoze out shines Linux is in its graphical interface, in that higher optical resolutions are atainable in windoze. This does not matter to most of us, but to gamers this is very important.
I keep Knoppix 'run-from-cd' Linux on hand to help me get out of trouble or fix some friend's computer software problem. Knoppix is probably the best Linux of this variety ever and gives quarter to none, to the best of my knowledge.
About the PC system, it really does not matter until you get into areas such as wireless Internet, sound and such. Any old or new PC works well, at least for me, with Linux of any variety which I have tried. Thus, what ever PC or laptop you have will accept Knoppix Linux. Most, if not all, will run faster as well. Just remember, as my freind Jerry Sharp used to say: "Linux does not have its 'hood' welded shut", a mechanic can fix it, more than can be said for windoze.