I use a batch file (*.cmd) that calls
isql -S ServerA -E -Q"sp_password null, new, sa" >> change.txt
with a line for each server, add a server add a line, change the pwd (search and replace). Low tech, but bulletproof and works well.
You could write something more complciated, read list of servers from a db, file, etc. and loop. DMO.ListAvailableServers is blocked on our network after the slammer worm, so that doesn't work.