I don't have any kind of guide. Didn't really think one was necessary. Here's the gist of it.
1. Install the development environment (compiler) on SME. (Search the forums as this has been explained multiple times.)
2. Obtain the patch(es), read the docs that come with them, and follow their directions.
If you want to integrate the patches into SME, you may have to develop a custom template. For example, the smtp auth send patch needs a qmail control file called smtproutes_users (ie, /var/qmail/control/smtproutes_users.) You can just create the file, or you can make a template, create new email properties in the necessary databases, develop new admin console screens, etc. How far you want to go with it is up to you.
I work in a cookie cutter environment, so I don't really need the template. You'll have to decide how much (or little) you need to do.
Scott