What do you mean, exactly? If you're asking about a distribution for thin clients,
http://www.linuxfromscratch.org can be good for custom jobs. Knoppix can be handy for diskless stations that have decent RAM and a CD drive, and there are countless distributions aimed at being used for converting old/cheap PCs into X terminals.
As for computers, just search for 'linux embedded' on Google and you should find plenty of reading matter and manufacturer sites. Many thin clients will run Linux perfectly well; the main issues are usually the ethernet card and the video card and Linux tends to handle both quite well. Nowadays it's not difficult at all to buy a thin client made with Linux in mind, because of it's suitability for mainframe-esque applications and terminal emulation.