My husband is flying to Arkansas next week to re-establish domicile. He is flying Dublin- London- Chicago- Fayetteville; first leg with Are Lingus, the rest with US Airways. I know that US Airways charges for bagage these days, but Aer Lingus doesn't. Normally, you get your boarding passes in Dublin for the whole journey, and only need to take your bagage through customs in Chicago, ie you don't go to a ticket counter. Where wil my husband have to pay the bagage charges, or do they not apply because the first leg is with another carrier? What about on the way home?

Call the airline and ask them.

I just recently returned from Australia and flew using Qantas. Upon arrival into the US I boarded American Airlines - they didn't charge me for any of my luggage. I wouldn't call unless you really want to pay. Otherwise you're bags will go straight through as they normally would.

I agree with this last statement.
I've travelled with excess luggage MANY times and have only paid twice - once internationally and once during a domestic flight.