Biggest resort on the Costa Dorada is Salou. You'll have no problems speaking to the locals - they all speak English (or they did when I was there in 1995). There's also Port Aventura just outside the resort - a great day out. It's like the Costa Brava but with better beaches. As for being a veggie, I'm sure you'll find some rabbit food in the many supermercados! If you stay in an hotel, there's always a salad option on the buffet. ;-)
If you're young and want nightlife, then Magalluf/Palma Nova is the place to be. If you want (relative) peace and quiet, and welcoming to British tastes, then go to Cala Bona on the east coast - my favourite resort on the island. Next door, Cala Millor is, these days, mainly German. Having said that, I've been to both resorts at least 7/8 times, so I may be biased.
