Which version of the Arduino IDE are you using?
Arduino 1.0.3
now one problem:
In file included from DS1307.cpp:3:
C:\Dokumente und Einstellungen\Keller-PC\Desktop\Arduino\libraries\DS1307/DS1307.h:55: error: 'byte' does not name a type
DS1307.h
41 // library interface description
42 class DS1307
43 {
44 // user-accessible "public" interface
45 public:
46 DS1307();
47 void get(int *, boolean);
48 int get(int, boolean);
49 void set(int, int);
50 void start(void);
51 void stop(void);
52
53 // library-accessible "private" interface
54 private:
55 byte rtc_bcd[7]; // used prior to read/set ds1307 registers;
56 void read(void);
57 void save(void);
58 };