Don't bother with the naysayers... Linux isn't difficult, it's simply that for Windows "power users" accustomed to doing things in very different ways than things are handled in Linux.
I'm not too familiar with Thinkpad hardware, but from what I hear they're well supported in Linux distributions because of IBM. I'm sure you'll be using wireless, and in the past it's been rather sketchy because of incredibly poor vendor support. However, just recently a company released a wifi stack to the Linux kernel, and compatibility is getting better all the time. However, since it's a Thinkpad I doubt you'd have much trouble.
When it comes to Linux, very basic things like installing packages are radically different from Windows, as the post above me frustratingly expressed. On any distribution (distro for short) worth its salt, there will be a "package management" system. Essentially, distros have repositories of thousands of programs, and so you only have to use one program to install any program in the repositories. On rare occasion, you won't find a program in a repository and you want to download from X site, there are a ton of Linux forums to help you install anything. If you have a problem, instead of getting frustrated, it's best to get on IRC or post on a forum because it is rare that you will have a completely unique problem no one has encountered before.
There is also the question of GUis. On Linux, there are lots, and it can be a big decision on what programs you use and in general what you find usable. You can check Google Images for KDE, Gnome, XFCE, Fluxbox, Blackbox, Enlightenment, and the beautiful-but-alpha XGL. The two main ones, and most "complete" (some say "bloated"), are KDE and Gnome. I say it can be a "decision on what programs you use" because for the most part programs use either the KDE libraries or those of Gnome. Therefore, if you want to AmaroK, a music management program based on the KDE libs, in the Gnome desktop environment, you will need the KDE libraries installed. This really isn't a big deal and only affects memory (more libraries loaded into RAM), but if you have at least 256MB it won't be an issue.
As far as alternative programs go, unless you're using an obscure program that is Windows-only, you can generally always find a suitable replacement for programs you're habituated to in Windows. OpenOffice is excellent, but its PowerPoint equivalent isn't as advanced as PowerPoint nor does it open complicated PowerPoint slideshows well, which I'd define as sound files, transitions, etc. Simple text-and-background presentations it usually doesn't have a problem with, and it's getting better every day. Similarly, its reverse-engineering of Word .doc files is very, very good.
I haven't used StarOffice, nor have I used KOffice, another Office suite available, but O
rg is held to be pretty much the best among the community. Try it on Windows and see if it suits you. Of course, if you're already using mostly open-source programs like Firefox and Thunderbird, then the transition is even easier and you feel more at home.
For beginners, I recommend Ubuntu. It's based on an excellent package management system (Debian), has excellent hardware detection, and has one of the best and fastest growing communities for support. I've been using it for over a year on my laptop, and at the beginning of May switched my desktop over to it as well. When looking at screenshots of distributions, please remember that the GUI you see can be changed entirely if you don't like it.
Partitioning isn't a big deal. Until you learn more about the Linux filesystem structure, I suggest you just partition 20GB for / (root) and the rest of the disk for /home, where your personal files will go. In Linux, swap space (the "pagefile" in Windows) is given its own partition as well, so I'd give 20GB to root, 1GB to swap, and 59GB to /home. If you are going to keep Windows for gaming (which, if you must play games that aren't available for Linux, I suggest keeping Windows partition because it's a pain getting them to work in Linux), install Windows first and then install Linux. Windows can be installed in 10GB partition and have plenty of room, so then just subtract that 10GB from your /home I suggested earlier.
LiquidNight is correct about Flash 8. Macromedia made no Flashplayer 8 for Linux. Thankfully, however, Adobe has just recently announced Flashplayer 9 will be available for Linux. And, unless you're running on obscure architecture, you rarely have problems with code compiled for a different system. You should just install the standard x86 distro, and there is no compatibility to worry about.
Good sites for constant perusal:
http://www.linuxquestions.org - Forums for many variations of Linux
http://www.ubuntuforums.org - Ubuntu-specific, excellent forums
http://www.tldp.org/guides.html - Great guides, from beginner to advanced. Check out the "Introduction to Linux - A Hands-on Guide."
http://www.linuxcommand.org - A site to introduce you to the command line. In Linux, you really do want to use the command line. It is incredibly powerful and you can get things done SO much quicker than with GUI. Trying to use command line in Windows is hairpullingly awful. In Linux, it's great.
That's not to say that I don't love the GUI, of course. Linux GUI is still worlds ahead of Windows, but not yet ahead of Apple.
Check out XGL videos...
I hope this post has been helpful. If you have any more questions, don't hesitate to ask.
