The Salzburg Information Office, Mozartplatz 5 (tel. 0662/88987; www.salzburginfo.at), is open in summer daily from 9am to 8pm and off season Monday through Saturday from 9am to 6pm. In addition to dispensing information, the office can book tour guides for you or make hotel reservations for a deposit of 7.2% of your total hotel bill (which will be credited), plus a 2.20€ ($2.85) booking fee.
There's also a tourist information office on Platform 2A of the Hauptbahnhof, Südtirolerplatz (tel. 0662/88987340).