If your friends cannot figure out a place to eat whilst in Vegas, then there is really nothing anyone can do to help them. Every chain and every chef worth his salt has at least 1 spot in Vegas. Since I live there, I will try to help.
I am going to assume they are going to stay at a strip hotel. They should eat in whatever highline restaurant is in the hotel they are staying at. As a guest of the hotel, they will have a much easier time getting a reservation/table. Also, make use of the hotel concierge service. The concierge may be able to get them reservations/tables at good restaurants at other hotels.
For a "real" Vegas experience, I recommend Battista's Hole In the Wall. It is on Audrie at Flamingo, 1 block east of the Strip (across from Bally's, behind the Flamingo). $15-20 per person, Italian food, and the former hangout of all the mobsters that used to run Vegas. All of the restaurant scenes in the movie Casino were based on events that supposedly occurred at Battista's. It has the right ambiance and the food is good.
If they like Sushi, Nobu at the Hard Rock Casino is sensational, but pricey. $75-100 per person, but everytime I have been there I have sat next to at least 1 celebrity.
Every great Steakhouse has a location in Vegas and they are all in the same general area, Flamingo and Paradise. Lowry's, Morton's, Roy's, Ruth's Chris and Del Frisco's are all very good, but they are all on the pricey side as well. Expect at least $50 per person, ranging to $200 for Morton's. Roy's would be an interesting departure for a Euro, as it is a Hawaiian Fusion Steakhouse. If red meat is not your thing, their seared Ahi is fabulous.
All of the novelty restaurants are in Vegas if they are shot glass or TShirt collectors (Hard Rock Cafe, Planet Hollywood, Harley Davidson Cafe, Margaritaville etc etc). They are fun places for tourists where you can generally have a decent meal for less than $20.
People always ask me about buffets and the answer is "I don't know". Buffets have ballooned in price over the last couple of years to the point that us locals no longer go (maybe that was the point). Most every buffet up and down the Strip is now over $20 for dinner, and the ones that aren't you probably don't want to eat at. The only buffet I attend semi-regularly is the seafood buffet at the Rio, $35 gets you all you can eat lobster claws, crab legs, whole dungeoness crab, steamed clams, raw or fried oysters, many different kinds of fish from tuna tartar to grilled swordfish and every kind of shrimp you can imagine, along with all of the other buffet trappings like prime rib, carved turkey, salad and dessert bar.
For Chinese, Chinois at the Forum Shops at Caesar's Palace is very good ($15-20 per person).
For pure overindulgence American Style there is the Cheesecake Factory, also at the Forum Shops in Caesar's ($15-30 per person). The menu is ridiculously huge as are the portions you will be served. The cheesecake is a must, but it borders on gluttony after a full meal in an oddly satisfying way.
There are a gazillion good Mexican places to eat in Vegas, Garduno's at the Palms is always good and reasonably priced, a good meal can be had for less than $10. And the Palms is always a cool place to hang out after eating for people watching/cocktails.
Another thing I recommend is keeping most (if not all) of your gambling at one casino, usually the casino you are staying at. Have your friends get a player's card and have the casino track all of their play. You don't have to be a high roller to earn free meals. Heck, you don't even have to win!
Lastly, if your friends get homesick, the best English pub west of the Mississippi is in Vegas, the Crown and Anchor (Maryland Pkwy and Tropicana Ave). They have Carlsberg, Tetley's, Boddington's, McEwen's, Old Speckled Hen, Guinness, Bass, Harp, Smithwick's, Newcastle, and many others on draft, you can also buy British cigarrettes like West and Rothman's. Plus they show all of the European soccer you could bear to watch and they have real dartboards, not electronic ones.
