This is usually not a starter issue, but replacing it is not too hard although, I have not done one on your model. I still think it is not enough juice getting to your starter. This is a shot in the dark but sometimes a good whack with a hammer on the solenoid can get your starter going again. If this works then yes you will definately need a new starter. But as I said earlier I still think this a lack of juice. A bad ground cable could definitely cause this as could a bad connection to the starter.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)