Use CloneCD (Get a Trial version here:
http://www.slysoft.com/en/) and the 'Protected Game CD' setting for Securom games! Works everytime for me! And the Reign of chaos cracks form GCW will work on Frozen Throne.
So install Reign of Chaos, then install Frozen throne, then update using the v1.17 update, then apply this crack WC3: Frozen Throne v1.17a [ENGLISH] Proper No-CD/Virtual Fixed EXE from GCW
P.S: And really if you want to play on two machines then you really by law need to own 2 purchased copies of the game! I know it sound silly but hey thats the law.