The R2 servicepack simply contains the files which have changed since the R1 release.
Simply unzip the file 2003r2us.zip into a folder named "2003r2us" - which is easily done by right-clicking on the file and chosing the according WinZIP function then. Double-clicking and fizzeling around with WinZIP is much more complicated.
After you have unzipped the stuff, open the folder 2003r2us. Then you will see a language container folder named "USA" in this case. Please open this folder, too.
Now you will see a bunch of files and folders which simply have to be dropped into your Calamus folder. That's all.