i'm pretty sure it would be fine.But I'm not entirely sure that an american hard drive would work on an English console, or if the core version only accepts 20gb?
at the end of the day, even though we use a different voltage to our
american friends, the innards of the 360 are nigh on identical.
as for the core only accepting 20GB? that's be a pretty dumb move by
M$ as they would be potentially alienating a lot of potential buyers of
the new 120GB drive.
my only concern would be of warranty. if the drive goes tits up, you'll
have practically no comeback.
it might be wise to contact the seller first and ask what their stance is
on returns and/or warranties.