Microsoft licensing can get complicated but there are basically two ways SQL Server may be licensed. One is by processor. When licensed by processor there is no limit on the number of users that may access the server. Unlike Oracle which licenses by core, SQL is licensed by processor socket so a quad core cpu still counts as a single processor. However processing licensing can get expensive, around $24,000 per processor for SQL Enterprise.
The other license model is to purchase a server license for each server and a client access license (CAL) for each user that will access the server. Under server licensing you can have as many processors as the edition of SQL Server you are using supports.
The licensing gets more complicated when you mix in virtual servers or a server that supports and Internet application.
Which model is best for you depends on how many servers and users you need to support. In my shop we run SQL Enterprise on five different servers with 600 users. All of our servers are multi-core and multi-processor. One of the reasons we use multiple servers is that in addtion to running business application we also do data warehousing. For us it turned out that that lowest cost licensing model was to purchase a license for each server and a CAL for each user. If we could consolidate everything on to a sinble box, processor licensing might be a better choice.
We also use Strataframe ES. Under the terms of MS licensing, the ES server acts as a concentrator, presenting multiple ES users as a single user to SQL. Although there is only a single SQL user, a SQL CAL is required for each user that accesses the SQL box via the ES server. You can't get away with a single CAL. If the SQL box was licensed by processor, you could have an unlimited number of ES users.
In Gerard's case it sounds like he needs an acutal server on each laptop which requires either a processor license or server license with a CAL. If I were in this situation I'd first try to use SQL Express by splitting my database into multiple databases to get around the 4GB per database limit. If that wasn't possible I'd look at SQL Workgroup edition with one server license and one SQL CAL for each laptop.