The attached zip file contains only the modified version of the web.config and db.config for YAF. Note that this is a very old post and I didn't check YAF since than since we introduced our own forum system, so you will have to manually modify your version. The procedure is simple - you just have to download both MonoX and YAF, install MonoX, than install YAF in a virtual folder below MonoX installation. At this point the two packages will work independently - web.config modifications allow YAF to start using MonoX users and roles.
As for the config files in YAF, the files attached can still serve as a blueprint. Just add MonoX DB connection string to YAF db.config (just as it was done in the attached file) so it can access MonoX database. You will have to comment out some of the config sections in the YAF web.config since they are already declared in MonoX. After that, make sure that a validation key and a decryption key for the machineKey are copied from MonoX web.config. Name attribute of the forms node should also be the same in both apps so YAF could pick MonoX' authentication cookie. Add MonoX role and membership provider, remove the httpHandlers and httmModules that are not needed in YAF, and that should be it.