You could try having a play around with the import/export function in address book (back up your address book first in case it goes pear-shaped! - In address book go file>export>address book(.wab) and save it somewhere that you'll be able to find it again!):-
First save your excel file as a .csv file. Then using the import function in the address book you will be able to import these addresses and then create your group.
I have just had a quick play around and this does seem to work, but I can't seem to get the addresses to go straight into a group.
Unfortunately, I don't have much time at the moment, so will have a look later and see if I can come up with something better (unless of course, you have got enough info. here to steer you in the right direction!).