Hey there, there is quite a bit of work in Dublin, however, during the summer, it gets really busy with people coming over for the summer... Depending on what kind of work he's looking for, his best bet would be agencies (for any proffessional jobs). However, for just a summer, might be quite hard for those types of placements... Maybe he can drop in a lot of resumes in town.
He can try "irishjobs.ie" or "loadzajobs.ie".
Hope that helps. For accomodation, definately try "daft.ie"... Hope this helps, G'Luck!