In this video Corey from IDParts.com replaces the alternator on a Mk4 Jetta TDI with the ALH engine.  This will be the same procedure on a Mk4 Golf TDI and New Beetle TDI with ALH engines, though the New Beetle will have less room and may require more disassembly.

Step-By Step

1. Disconnect battery from car.  This is the first step whenever performing electrical work on your car.
2. Remove engine cover
3. Remove upper intercooler pipe
4. Remove lower belly pan and passenger side skirt
5. Remove serpentine belt
6. Remove Large Cooling fan.
7. Remove A/C compressor from bracket.  Do not disconnect A/C lines.
8. Remove serpentine belt tensioner.
9. Remove Alternator and disconnect wiring harness.