how to do md5sum on windows xp
download a copy of md5sum.exe to c:windowssystem32
(I got mine from http://downloads.activestate.com/contrib/md5sum/Windows/)
open command prompt (start -> run -> ‘cmd’)
cd to the directory where the file you want to check is e.g. cd c:downloads
type md5sum filenameoffileyouwanttocheck.foo
This will return a string of numbers and letters – compare to the one listed against the file you downloaded (i.e. the one usually listed somewhere on the page where you downloaded the file from)