Hi Cerebral.
I did two things to get past this:
1) I used instructions other than "Life with Qmail" - great instructions only they didn't work on my configuration of SuSE very well. Instead I used the following
2) I made sure that I was in the appropriate directory when applying the patch. In my case, I needed to go the the directory where I had un-tarred the source files and apply the patch there. This source directory is not to be confused with the 'SRC' folder that has all the C files designated by filename.h; rather, you need to be in the folder where you un-tarred your original qmail files (or whatever files you are attempting to patch.)
Hope this helps or that you alread have found a solution.
Truly,
ServerStorm