laptop Internet addresses.

[pjw at usna.navy.mil]

Laptop PC's and Unix boxes will be upon all us administrators soon.
Complete with Ethernet interfaces. My question: how do you assign
Internet addresses to people who may plug into different subnets on
different days ? If you give them multiple addresses you could eat up
a lot of address space in a hurry ?

This is going to become a potential hassle in the next year or two. 
How are people going to deal with it ?

Our case: we have classrooms on a different subnet than faculty offices.
Laptop PC's in the offing. Sun servers on both subnets. How do I deal with
100+ PC's that could be on either of my two subnets ? How about 4000 PC's
plugging into any of the 30-50 subnets in the school ?