Yanbu is a pretty small town compared to Jeddah, Riyadh or Dammam and there is very little choice in long-term accomodation.
Western expatriates live on 'housing compounds' and have a life that can be insulated from the Saudi environment around them. Although these western compounds still have the tough security perimeter and armed guards they were given after a single shooting incident there in 2004, Yanbu is pretty safe these days compared to the rest of Saudi.
Yanbu is divided into two main areas. There is the Royal Commission, which is residential to the North and industrial to the South. The RC is all newly-built, clean, organized and very western. This is where you will find the western-style shops, schools and hospitals. It's also probably where you will work.
The other area is Yanbu town, which is about 15 Km away to the North. This is the original Arab town and is quite interesting, but is chaotic and a little dirty compared to the RC which is spotless. It's perhaps also a little less safe than the RC, certainly for an unaccompanied westerner on foot.
Where you live will depend on your company. They may have their own company accomodation compound if they are big - but then you will be mixed in with a lot of other nationalities, most of them Indian, Pakistani and Filipino. There are two privately owned luxury compounds in Yanbu with villas for rent and you should go for them if you have any choice. All but the lowest salaried western expats live on this type of compound. The first is Arabia Homes. It's fairly compact and quite a long way out from the areas where most people work and shop. It's out in the desert past Yanbu old town. The drive to and from there can be a bit scary, particularly at night. Arabian Homes is ok, but it's an old compound and looks it. They are also fairly free with who they rent to, so expect to see veiled ladies around the swimming pool. The other compound is The Cove. That is within the RC and has a large lagoon and 2km of white beaches actually completely within the security perimeter of the compound i.e. no threat even from the sea. It's also a lot bigger and has a strict westerners-only policy. Prices are about the same, but you may have trouble getting a place in The Cove. It's a new compound scheduled to open in Jan 2010, but it's already very heavily booked.
As regards schools, there is really only one suitable for American and European kids, and that is the International School of Yanbu. It's also on the Royal Commission. Although it's an American school, they have an arrangement with the local British-Indian school for O-levels and A-level exams.