While there are few standards published it seems, we can use some guidelines that can then be adjusted based on your environment. Let's take teh number of PCs per technician as an example. I have seen numbers range from 25 to over 100 PCs supported per technician. The nature of the user and software applications being used often drive this ratio. A standard Windows 2000/Office 2000 image rolled out to 1000 users probably will require fewer technicians/PC than a custom application.
Another factor is location. Are all users in one location or are you spread out? Current installed hardware and software base can play a large roll in staffing levels. If you have a lot of different hardware, then creating standardized images can be difficult leading to the need for more staff.
User training level, complexity of applications, custom development, hosting email/web server in house all will be a factor in determining how much staff is needed. If you have the right people with the right skill sets and are still falling behind, then you probably have the data needed to justify additional staff. It may take some work to pull it all into a usable "numbers based" format.
For what it is worth, my departent support 437 PCs, 22 servers including email, 2 web servers, file/print server, 8 Citrix servers IP based telephone/voice mail system and SQL server plus associated switches and routers across 19 locations in a 1000 square mile area. We do that with 5 staff including me.