I believe the COA's without install disks are for system builders who instead of including a actual Windows XP install disk with the system, include a system restore disk instead similar to what the Compaqs, Toshibas, Gateways, etc. used to come with...... (I say used to because not sure who still does it, I know HP has went to just having system restore on seperate partition of hard drive without a cd for recovery............stupid IMO, but whole different topic

) but I would think it would work the way you are intending it to use it, seems like it would be legal all, as the main thing would be that the key code would be unique to your system.
Shawn