[Sheap]

Slackware is a little more oriented to the advanced user, but I learned on Slackware (back when it was still the #1 distribution). If you are used to working in a commandline environment then you will be OK. You don't need to know any programming to set up or use the system, but if you do have some programming ability you can do additional things that you couldn't do otherwise (but this is not specific to Slackware, it's true of all Unix).

I use Slackware myself, primarily because it is very tolerant of being altered. Many distributions get a little antsy if you start tinkering with their stuff.

As far as Linux vs. NT/XP filesystems:
Linux has its own filesystem, called ext3. (There are other filesystems around, but this is more or less the "standard" one). Windows XP uses NTFS, which is called NTFS because it was originally developed for Windows NT. Files stored in a Linux ext3 filesystem can't be accessed by Windows, and while Linux can read NTFS, it can't write to it, at least not to recent Versions. It can both read and write DOS and Windows 95/98/ME filesystems. (And there are third-party commercial programs for both Windows and Linux that allow full access to the other OS's filesystems, if you really need it).