hi, my dad has asked for one for xmas. However, they are a bit expensive for me on my own, so my sister is going to go in with me. She lives in the USA and is coming over for xmas - if she bought one there, would it be compatible here - would there be any problems?
As Gingejbee states, there will no technical problems. However, if your sister is going to be bringing other gifts into the country she needs to remember that she's likely to have to pay tax and duties if the total value exceeds £390.
Just for clarification (and to point out that there's no conflict between my post and VHG's):
I was assuming that the drive would be USB-powered. Any drive, purchased in the USA, which is MAINS powered will require 120V (at 60Hz), whereas our mains system provides 230V (at 50Hz).
If in doubt, buy from the UK, so that (irrespective of the power system) you'll have no worries about compatibility.