I'm going to make some tutorials really soon - now that you're requesting, I'll probably just make them tonight. I'll post the link here once I'm done.
edit: I've already got some done (including a tutorial on how to install the grenade launcher mod) here: http://www.gtagaming.com/downloads/installation-help
later on im going to do a texture mod like the johnny klebitz one
edit2: alright the texture mod tutorials are done too, i hope that helps.