This might be a little over-the-top for your requirements.....but:
I usually find that when dealing with "commercial" IT projects, that most suppliers/consultants will be familiar with the standard project "methodologies". These are industry-standard processes used for creating, managing and implementing large scale projects.
Personally I use SSADM (Structured Systems Analysis and Design Methodology) but there's PRINCE2 as well....
Anyway, a good primer on SSADM can be found here:
http://www.comp.glam.ac.uk/pages/sta.../chapter4.html
HTH!