Linux will techinically run on pretty much any hardware, from 386 onwards (in the Intel range), as well as some Macs (YellowDog, Mandrake-PPC), etc. I have read something about getting it to work on i286 (but not 8086s). It'll run on Sparcs, Alphas, DECs (I'm not quite sure about the distinctions between these as I've only ever used it on an Intel based system). Sometimes, however, you may need to install it onto another system first, manually configure the kernel for the new system and then install onto the new system.
There is normally a readme file (or something) that's on the installation CD that should tell you what basic system that particular distro requires.