Within Sweden, most people speak English, but do try to learn a few words/phrases before you go... I do recommend the Berlitz book for a quick session.
Some Swedish words to get by:
HEJ means hello. TACK means thank you. JAG BJUDER means it's on me. VAD KOSTAR DET? means how much does it cost? DET ÄR FÖR MYCKET! means that's too much! VILKEN PUDDING! means what a babe! HJÄLP is pronounced YALP (in American english) and means help! VI SES means see you.
If you're lost, or just want to know any good restaurants in the area - don't hesitate to ask! Swedes LOVE to speak English and will help you if they know the answer. This is a problem for foreign students who often have to ask their classmates NOT to speak English to them, because they're not learning any Swedish.