I see my colleague Preston Gralla is looking for the best Linux for a Windows pro. That's a good question with several good answers.
Preston's son Gabe gave him some excellent advice when he recommended Wubi. This is the Windows' world easiest Linux installer. With it, you install Ubuntu 8.04 just like it was any other Windows application. Download it, click the install button and let it rip.
It installs Ubuntu, from the Windows' user viewpoint as a single directory. You don't need to re-partition your hard drive, burn a CD, or do anything that any Windows user doesn't know how to do. Once installed, the next time you reboot your PC, you'll have the option of booting into Ubuntu as well as XP or Vista. If you don't like it, you just uninstall it just like any other Windows program. No fuss. No muss.
Rebecca Sobol, vice-president of LWN.net, formerly Linux Weekly News, who ran a birds of a feather meeting at LinuxWorld last week on how to pick a Linux distribution, agrees that Wubi is a good choice. Sobol added,"For live CDs, Knoppix is still a good choice. Most of the major distributions also have a live CD, usually with an installer that you can click on if you want to actually install it, but then you have to deal with partitioning if you don't want to wipe out Windows. You can try out Ubuntu, openSUSE, and many others with a live CD. You can also get a live USB key with the latest from Fedora, Mandriva, and others."
LWN also has a good listing of Linux distributions broken down into several different categories. For example, if you want a Linux designed for a specific country or architecture, the LWN list is a good place to start. If you want to know everything about what's what in the latest Linux distributions, DistroWatch is the site, but its sheer mass of detail would overwhelm most Windows users.
Personally, for Windows users, I usually recommend a distribution that, unfortunately, doesn't come in a bootable USB or CD version: Xandros. I like Xandros for people who are comfortable with Windows because, with its customized KDE 3.4.2 desktop it looks and works a lot like XP Pro.
The resemblance is more than skin-deep. Xandros also includes support for writing to Windows' NTFS, authenticating with AD (Active Directory) and Microsoft Office formats.
Xandros, however, unless you get it in an Asus UMPC (Ultra Mobile PC), is one of the few Linux distributions that you must pay for. There was a free 'as in beer' version, called Open Circulation, but it no longer seems to be available.
The free version will be available again. After Xandros acquired Linspire, the company announced that it would be making Freespire, the foundation for future versions of Xandros. However, that version of Freespire is still being developed.
A final concern for Gralla is that he is going to be trying Linux on a ThinkPad T41. That's a five-year old laptop running a 1.6GHz Pentium M processor. If it's running the default hardware that means it only has 256MBs of RAM. That's more than enough for desktop Linux, but you can forget about trying Linux desktop fanciness like Compiz 3D graphics on this laptop.
Wi-Fi on the T41 shouldn't be a problem. Most of the T41's use Intel's 802.11a/b/g PRO/Wireless LAN 2100 3B Mini PCI Adapter. Most Linuxes come with the firmware, ipw2100, they need to work and play with this Wi-Fi adapter.
However, the T41, like a lot of computers of its vintage was build right as USB 2.0 was coming in and its USB ports, for all practical purposes, run as USB 1.1 ports. This matters for Linux because you really can't, in my experience, run USB-based distributions on 1.0 or 1.1 ports.
All-in-all, what this means for Gralla is that I'm recommending Wubi for him, followed by Xandros. If you're a Windows user with a newer system, Wubi is still at the top of my list, with Xandros following closely behind, but you can also safely consider a live CD or USB stick-based version of the latest stable versions of Ubuntu, Fedora, or openSUSE.
Good luck to you Preston, and to all the rest of you who want to give Linux a try on your Windows PCs.