Russ Nelson's open-smtp patch

[Michael]

Can anyone explain how to install Russ Nelson's open-smtp patch for 
qmail?

I am interested in patching my qmail installation to allow relaying for POP3 
authenticated users.  I have downloaded the code, but the README just 
says to patch checkpassword, but I am unfamilar with patching programs.  
Additionally, there are 2 checkpassword.patch files in the tar:

checkpassword.patch
checkpassword.patch~

Would anyone mind explaining the patch process?  (Russ :) ?)

Thanks,
Michael Lundberg