If they are doing web development with anything earlier than visual studio 2010 they are going to need to be administrators of the machine so that they can debug processes running under a different user context. Most of the time this means debugging web apps on IIS. If they switch to 2010 they can use IISExpress instead. If they are doing anything that can be construed as system programming they will need admin access.
A good idea might be setting up a development forest that they can use virtual machines to do dev on. Developers also use email, calendars, and the like...try to keep those duties separate without deploying two workstations.