WGA is no problem. Also, you can easily install a single (OEM) license on multiple machines or partitions (the latter is completely legit in EU) without any problems. Telephone activation may be necessary after the first couple of installs but there is no problem to be expected. You should also be able to call the activation in another country as well.
Initially we've used a single OEM key to install dozens of XPs with telephone activation - no problem at all. (Yes, we do own more than enough licenses but the same key for all solves a few problems - have changed to a single VL key since.)
