Documenting a giant web of inter-related stored procedures in an MS SQL database: What tool or format?
The most important thing about documentation is that it makes sense to you.  There's no really standard way of doing this.

If you've got lots of stored procedures that all connect to each other starting with a Visio diagram with one object for each procedure, then links between them so you can track how things go from procedure to procedure is probably a pretty good start.