Personally, I tend to use AntiSpam to block the majority of it at the
server, then Pluto's filter system to block the rest of it at the client.
Anything that gets through that lot is then forwarded to Spamcop.
Of course, since you are using M$, that won't be of any use to you, but
then programs like these do exist on Windoze. Try asking in one of the
groups that supports Windoze and they should give you a few names.