>>2
That's strange. In 2001 I used to develop software professionally on a 400Mhz system with 256MB ram, using 2k. No, it was not slow in the least, other than the obligatory long boot time.
If you want a fast Windows OS for a 64MB machine, I recommend Win98 with the IE components removed and the explorer replaced by Win95a's. Plain 98 is dog slow, almost entirely thanks to that infernal default shell.
If you go the *nix route, and don't wisely use NetBSD, then linux 2.2 with X and something like WindowMaker, OpenBox, or similar will work. Do not install KDE or Gnome. Further, you'll want to stay away from GTK2 apps and most QT ones. GTK1 is about your only option outside of things like Athena and the ilk. Perhaps replace Bash with something smaller, like Ash.