Hrm...
after reading and re-reading it.. it sounds legit to have 1 licence for all 3 users ONLY IF they dont put their drive into another computer. (which would fail anyway because windows xp would sense new hardware and know it was on a diff computer)
It seems legit because only one person can use the computer/OS at a time. It would be like creating 3 profiles on a computer, and splitting the 3 profiles across 3 drives. All are valid users... but cannot be running at the same time.
that's just my take. Microsoft could see differently for a reason I haven't thought of.
- rp