For many, Linux means giving old PCs new life. Old PII machines to those that might just be missing a hard drive. No matter what ails it, if it works it likely can run one distro or another. In my own home, I have a couple of older boxes running Puppy Linux and one old Zonbu mini, now running Ubuntu that acts as a POPFile server. Yes, I am using SSL and also SSH into my home network when I am away. Not stupid enough to use POPFile across the Web like that without some kind of security in place.
But for some, the question remains as to just how slow a Linux box can actually go? I mean, PI with 32MBs? Is it possible? Short answer, yes, but not likely with any windows manager that I can think of at the moment. What is the idea box to turn into a router? I would say a PIII with at least 256MB of RAM might do it. But like with anything, more is always better. And remembering that recommended requirements will always serve you better than minimum.
Which is the best distro for older PCs? Honestly, if it is really old, I am going to say over and over that Puppy Linux wins every time. I have used other distros designed for older PCs and I always come back to Puppy as it is just easier to use. My time is limited, so I rather not spend a lot of time “configuring” when I have a distro that does most of the heavy lifting for me already.