1. Yes, you will have to unscrew a panel somewhere on the bottom of your laptop to install a mini-PCI card but it is not hard or dangerous;
2. There is Intel 2200 Source Forge project as well ( http://sourceforge.net/projects/ipw2200/
) but the 2100 project is much more mature and stable.
3. You can ask IBM about 2100 (when they can have it), or maybe just about the white list issue (what 2100 card will work in your laptop of you buy it from a different reseller).
4. Yes, you can always buy a PCMCIA card but if you know that there is a particular card that will certainly work with your PC and your distribution, I think it is better to look for 2100 (or 2200). You may try 2200 - as I can see, the project is very active, so if there are some bugs, they will surely be fixed very soon.