http://iso.linuxquestions.org/
Good place to get LINUX.
P1 is too old.
Linux was designed for a 386. I think a P1 can handle it. The question is how many bells and whistles can you run in addition to the kernel.
Go here to see distros that are designed to run on computers that old. You'll notice i586 (Pentium I) is selected, so try 486 and even 386 for distros that will definitely run on your system.
Watch out, many older systems won't boot from CD.