It's a low-class computer we were just going to throw out, so I took it and set it up for a server or two. I use it for backup as well.
It works fine, even on Ubuntu.
-sniperoonie-
Ubuntu uses 386MB minimum of RAM, good for an atom laptop. Wine probably uses some RAM, though.
Windows 2000 uses 64MB RAM and a 133MHz Pentium processor minimum, but you probably aren't used to using it or hate it. I don't really care about the UI, though. Also, a dedicated server of blockland probably might be able to run on Windows 2000 (someone should test this).
If a dedicated server can't run on Windows 2000, then it can most definitely run on Windows XP, which calls for 128MB RAM and a 300MHz Pentium processor.