windows 2003 CAL clarification

Here's what Microsoft say. It's pretty clear - you need one CAL per device/user that accesses the server software. You are using file and print sharing, hence one licence per user/device that makes use of these services. (Unless you use the per Server licensing mode - which may be more appropriate if you only have one server, and don't intend to buy any more - then the number of CALs that you need is the maximum number of simultaneous connections to the server.)