1. Go to http://ssd.jpl.nasa.gov/cgi-bin/eph
2. Press 'Target Body' and wait for the new page to appear
3. Under 'Select Major Body', go to the text box 'Lookup the specified major body' and type in 'Rosetta'.
4. Press 'Search'. The first page should reappear, showing 'Rosetta (Spacecraft)' in 'Target Body'
5. Press 'Observer location' and wait for the new page to appear
6. In the text field 'Lookup the specified City or Observatory, enter a reasonably large city close to you
7. Press 'Search'. If the city is not known, the system will tell you. Try again... If the location is known, the first page should reappear, with the 'observer location' filled out.
8. Press 'Time Span' and wait for the new page to appear
9. Select the time span you want to have plotted. For the maps I created I used AD 2005-03-04 20:00:00 to AD 2005-03-04 23:00:00 UT. For the 'output interval' I selected 1 min. The 'RTS mode' I left as it is ('none'). Don't modify the 'output format'.
10. Press 'Use Specified Settings' and wait for the first page to reappear.
11. If you want, play with the 'output quantities and format' - I ignored it.
12. In 'Select desired options', mark 'Suppress output during daylight' and 'Suppress output when body below horizon'.
13. Press 'Generate Ephemeris'. A web page with some header information and the actual data is created. The position you should be interested in is 'R.A._(a-apparent)__DEC.'. That gives the apparent position of Rosetta in Right Ascension and Declination, which lets you plot it in a star chart. Success!