Whenever I get a new Windows development machine, the first thing I do is install some software to actually make it usable. First off, it’s usually Cygwin.
This allows me to work on a Windows filesystem using a proper set of tools, including the venerable Bash shell. This shell has so many tricks and shortcuts up its sleeve, it’s incredible. One of my favourites (and one I always forget how to use in between using it) is variable substitution. The Win32 CLI offers a watered-down version of this as well, but Bash allows you to do things like this:
for i in $(dir *.MD5); do mv -f $i ${i%.MD5}.md5; done
Note the variable substitution bit in the curly braces, that says “return everything except the shortest match starting from the right-hand-side of the variable $i that matches the pattern .MD5.