Having downloaded DesignSpark PCB I think the activation code is for a single copy per PC, but reading comments on the DesignSpark website you can email them and ask for a second (or third ??) activation code if you want to run another copy on say a laptop.
Or you could register with their web site twice and get another activation code that way 
If anyone is interested, I've converted the EagleCAD Duemilanove to DesignSpark PCB format. I'll post it in the forum or to my blog later today.