I can attest to running with 64MB of RAM, that's why my system has now. It's also an AMD K6-2 266, pretty old technology. Anyway, I'm using Mandrake 7.1 with KDE. Running just KDE, gtop reports about 50 MB of RAM used with about 5 MB of swap. Running Netscape ups the total RAM usage to about 80MB. When I'm running a typical suite of programs (a few netscape windows, a couple terminal windows, text editor), I'm using around 100MB of RAM.
I also failed to mention that I'm also running Apache and MySQL on this computer, though only for development purposes, so that uses some RAM too.
Though the RAM usage seems bad, the performance isn't bad at all. It certainly runs better than Win98 does .