I don't know about just Linux, especially if your laptop is the only computer you usually have available to you. I'd probably go with the XP/Linux option, since you don't really lose anything significant, and you kind of get the best of both worlds.
As far as distribution goes, I'd recommend against something like Slackware -- especially for a laptop. I see absolutely no purpose in spending hours fighting to get things working that would just work if you pick a less "minimalistic" distribution like Ubuntu or Fedora. Personally, I'd recommend Ubuntu. It's the only distribution I use on my machines (I guess I still have Slackware on my servers, but that's mostly because I don't want to go through the effort of setting them up again), and it works beautifully.
When I used Slackware, Linux was a fun toy. Something to use when I was bored. After switching to Ubuntu, it became my primary operating system. There was no need for Windows. In fact, when I was in Windows, I felt like I was tied down. Ubuntu is a much richer environment for most tasks.
Aside from everything "just working" with Ubuntu (usually right out of the box, all of your hardware, including printers, miscellaneous USB devices, etc.), I'd say the most substantial advantage it has over something like Slackware is it has an officially maintained package system. If you expect some software to be installed (R, for example), you crack open a terminal and type the appropriate command, instead of just getting "idk wtf you're talking about dude" as a response, if it's software it knows about, it'll say "i know what you're talking about, but i don't have the appropriate software installed. type this to install it." It's beautiful. It's how things should work.
