Help with licening for SBS2003

I'm a little confused having read conflicting information about how the licensing for SBS2003 works. According to this microsoft link;

http://www.microsoft.com/WindowsServer2003/sbs/evaluation/faq/licensing.mspx

SBS2003 has per user or per device licensing. But I can find no place to choose which licencing model I wish to use.

I have a server I need to put more CAL's onto, but there are two sku's, one for per user and one for per device, and because I can't figure out how the current server is setup, I'm worried I'll pick the wrong one and cause trouble.

The network in question has 5 workstations, and lots of users (about 20 or so), but 15 of those users all use the one PC remotely (it has xpunlimited installed)

It would seem that per device licening would be ideal in this situation, but the licencing screen on the server says that licence usage peaked at 12.

While I'm at it, if the server reckons they've used up 12 licences but only has 5, does that mean that the server doesn't actually do anything when sites go over their user licences, or are there actual usage consequenses of not having enough licences? Seems weird that you can get to 12 only having 5?

Any expert suggestions on what I do?