I'd send the seller an email, asking if they know the sizes, i had a quick search on google, the only zeta wheels i found weren't multifit but just the one size :S
According to 'pimpmywheels' they're the same pcd and offset as the micra wheels but the c/bore is different. The astra c/bore is 56.5 and the micra c/bore is 59.0. I don't know what effect that has. I just want to know will they fit please.
Bigger bore is ok but there is talk of vibrations of the wheels don't centre properly. However I believe this is just talk as I haven't had any problems as the wheel nuts centre the wheels fine.
FYI renault wheels are the closest match I have found.